Warming-induced changes in benthic redox as a potential driver of increasing benthic algal blooms in high-elevation lakes

IF 5.1 2区 地球科学 Q1 LIMNOLOGY Limnology and Oceanography Letters Pub Date : 2023-10-31 DOI:10.1002/lol2.10357
Stephanie E. Hampton, Jill S. Baron, Robert Ladwig, Ryan P. McClure, Michael F. Meyer, Isabella A. Oleksy, Anna Shampain
{"title":"Warming-induced changes in benthic redox as a potential driver of increasing benthic algal blooms in high-elevation lakes","authors":"Stephanie E. Hampton,&nbsp;Jill S. Baron,&nbsp;Robert Ladwig,&nbsp;Ryan P. McClure,&nbsp;Michael F. Meyer,&nbsp;Isabella A. Oleksy,&nbsp;Anna Shampain","doi":"10.1002/lol2.10357","DOIUrl":null,"url":null,"abstract":"<p>Blooms of algae attached to the bottom of nearshore environments have increasingly been observed in clear, nutrient-poor lakes worldwide (Vadeboncoeur et al. <span>2021</span>). The phenomenon is puzzling for at least two reasons. First, such nearshore benthic blooms appear to be common across heterogeneous contexts—from the world's largest lake in Siberia to small mountain lakes in the Rocky Mountains of North America. Second, the blooms are enigmatic because they have been observed in the near absence of direct human disturbances, such as those in well-protected, remote mountain lakes. A recent review (Vadeboncoeur et al. <span>2021</span>) highlights the diversity of mechanisms through which these nearshore benthic blooms may be triggered—such as nutrient loading through atmospheric deposition or human activity within the watershed, changes in hydrodynamics associated with climate change, and food web alterations that reduce grazing pressure. Yet none of these potential drivers are common across the lakes where nearshore benthic algal blooms have been reported. Here, we suggest that a previously unappreciated driver is common across all lakes that experience warming associated with climate change—elevated nearshore temperatures that reduce oxygen and promote nutrient release from sediments under the biofilm. In principle, this phenomenon should be particularly notable in high-elevation lakes because water at higher elevation holds less oxygen at saturation, high-elevation lakes are warming more quickly than their lowland counterparts, and they can receive additional warming from relatively high solar radiation (Fig. 1). We briefly review the evidence in support of this concept, recognizing that the data necessary to rigorously test it do not yet exist; however, such data collection is feasible.</p><p>Algal taxa in oligotrophic systems are well adapted to naturally high-light and nutrient-poor conditions (Cantonati and Lowe <span>2014</span>). Because nutrients at the sediment–water interface can be rapidly cycled, nutrient concentrations in the water column may not be reliable indicators of nutrient availability for benthic primary producers (Vadeboncoeur and Power <span>2017</span>). Hot spots or hot moments of elevated nutrient concentrations in littoral regions favor green algae, leading to thick filamentous mats (also called filamentous algal blooms; Oleksy et al. <span>2021</span>; Vadeboncoeur et al. <span>2021</span>). These periphyton blooms appear to be an emergent response to changing environmental conditions in oligotrophic systems, yet the ultimate drivers behind their increased occurrence are debated and often obfuscated by confounding processes. For example, in Lake Baikal, increasing evidence has pointed to highly localized wastewater inputs leading to increased <i>Ulothrix</i> spp. and <i>Spirogyra</i> spp. abundance (Timoshkin et al. <span>2018</span>; Meyer et al. <span>2022</span>). Similarly, Lake Tahoe has experienced increased periphyton biomass likely due to a mix of wastewater-associated eutrophication, groundwater leachate, and complex physical and hydrological processes (Naranjo et al. <span>2019</span>; Atkins et al. <span>2022</span>). Although observations of increased periphyton blooms in lakes with adjacent human population can draw links between human activity and in-lake periphyton responses (e.g., Rosenberger et al. <span>2008</span>), these blooms also appear to be increasing in remote, high-elevation systems that lack permanent human settlements (Oleksy et al. <span>2020</span>).</p><p>High-elevation lakes located in mountainous regions are frequently characterized by low-nutrient concentrations, long periods of ice cover, high solar and UV radiation, as well as heterogeneous landscapes associated with complex topography (Moser et al. <span>2019</span>). Despite their remote locations, historically oligotrophic high-elevation lakes have experienced primary productivity increases that sometimes have been attributed to global change, including atmospheric deposition of reactive nitrogen and phosphorus, species introductions, and climate change (Ballantyne et al. <span>2011</span>; Saros et al. <span>2011</span>; Catalan et al. <span>2013</span>; Brahney et al. <span>2014</span>; Sadro et al. <span>2018</span>; Vadeboncoeur et al. <span>2021</span>). Most of this literature describes changes to water column productivity. However, numerous studies have shown that the frequently neglected benthic habitats of oligotrophic lakes, including those at high elevations, dominate ecosystem processes of primary production and respiration (reviewed by Vadeboncoeur and Power <span>2017</span>). Changes in benthic algal assemblages previously may have been overlooked. For instance, within lakes in the southern Rocky Mountains of North America, sediment records indicate that nearshore algal assemblages have changed appreciably in recent decades, with 200–300% increases in periphytic green algal species (Oleksy et al. <span>2020</span>).</p><p>Although sources and magnitude of nutrient inputs vary greatly across lakes worldwide, a common factor is warming associated with climate change (O'Reilly et al. <span>2015</span>), which can promote oxygen depletion (Jane et al. <span>2021</span>). Mountainous regions are warming faster than adjacent low-lying areas (Pepin et al. <span>2022</span>), and warm water holds less oxygen than cold water. In a high-elevation lake, relative to its lower elevation counterparts, the water column holds lower oxygen at saturation due to the inverse relationship between elevation (atmospheric pressure) and the oxygen capacity of water (Fig. 1). Hutchinson (<span>1957</span>) briefly alluded to the potential for this elevation–oxygen relationship to alter benthic ecology. The importance of not only oxygen content but also partial pressure is increasingly recognized as affecting biodiversity patterns among aquatic invertebrates (e.g., Verberk et al. <span>2011</span>). Our mass balance calculation using a vertical 1D reaction–diffusion model suggests that elevation effects on oxygen in a warming mountain lake could account for sediment anoxia occurring days to weeks earlier than would occur in a warming lake at sea level (Supporting Information). High solar radiation in mountain lakes can contribute to additional warming, and nearshore temperatures can increase markedly relative to the offshore. In some cases, as nearshore temperatures warm, a thermal bar may develop, reducing mixing and allowing littoral water temperatures to become even warmer (Vadeboncoeur et al. <span>2021</span>). Warming sediments can quickly stimulate heterotrophic microbial processes that consume oxygen (Bergström et al. <span>2010</span>). Convective cooling in the littoral zones can further limit horizontal exchange of oxygen and nutrients with offshore waters (Doda et al. <span>2023</span>). These combined factors could explain why mountain lake nearshore blooms have been so noticeable in the absence of other clear drivers.</p><p>Warming littoral zone temperatures can decrease oxygen available for aerobic metabolism, creating an environment more favorable to anaerobic metabolism just a few millimeters into the sediments (Fig. 1, Schlesinger and Bernhardt <span>2013</span>), particularly at night when photosynthesis does not produce oxygen. Microbial consumption of oxygen in sediments frequently exceeds the oxygen supply through diffusion (Fenchel and Finlay <span>2008</span>). Without oxygen, microbes cannot use oxidative phosphorylation to convert organic matter into CO<sub>2</sub>, and instead must rely on the alternate electron acceptors including nitrate (<math>\n <mrow>\n <msubsup>\n <mi>NO</mi>\n <mn>3</mn>\n <mo>−</mo>\n </msubsup>\n </mrow></math>), iron (Fe<sup>3+</sup>), manganese (Mn<sup>4+</sup>), and sulfate (<math>\n <mrow>\n <msubsup>\n <mi>SO</mi>\n <mn>4</mn>\n <mrow>\n <mn>2</mn>\n <mo>−</mo>\n </mrow>\n </msubsup>\n </mrow></math>). These alternate electron acceptors are exploited sequentially based on their energetic favorability and produce electron donors including reduced bioavailable forms of carbon, nitrogen (<math>\n <mrow>\n <msubsup>\n <mi>NH</mi>\n <mn>4</mn>\n <mo>+</mo>\n </msubsup>\n </mrow></math>), iron (Fe<sup>2+</sup>), and sulfur (H<sub>2</sub>S) that may diffuse into overlying oxygenated water (McClure et al. <span>2021</span>). For example, nitrate and ammonium become bioavailable in locations where oxygen conditions fluctuate and allow temporal and spatial coupling of the anaerobic and aerobic metabolisms involved in nitrogen cycling (Davidson et al. <span>2000</span>). In addition, oxygen-depleted water in the sediments can result in high phosphorus concentrations because ferric iron reduction (Fe<sup>3+</sup> to Fe<sup>2+</sup>) coupled with slightly acidic pH conditions (particularly at night when photosynthesis ceases) releases bioavailable forms of phosphorus (Gotoh and Patrick <span>1974</span>). Importantly, diurnal heating of sediments in the littoral zone can drive water movement within surficial sediments, creating convection of pore water that may further increase availability of bioavailable nutrients to periphyton (Axler and Reuter <span>1996</span>).</p><p>Altogether, the fluctuations in oxygen availability and temperature in littoral zones can increase availability of nutrients released from sediment, where they are efficiently intercepted by periphyton (Carlton and Wetzel <span>1988</span>; Dodds <span>2003</span>) and may not become elevated in the water column (e.g., Rosenberger et al. <span>2008</span>). Complex successional patterns, such as diatomaceous mucilage production can initiate an early, physical barrier between the water column and the sediments (Hoagland et al. <span>1982</span>; Wood et al. <span>2015</span>). As the biofilm undergoes colonization and succession, warm temperatures may accelerate heterotrophic processes, thereby promoting biofilm growth and further impeding exchange between the water column and sediment. Most importantly, nutrients released from the sediment are directly used by periphyton in the mat, and do not reach the water column; concurrently, the biofilm impedes movement of oxygen from the water column into the sediment, promoting anoxia which encourages nutrient release.</p><p>Once a robust biofilm is established, periphyton blooms can promote an environment that is favorable for their further growth—both by stimulating internal nutrient release (Carlton and Wetzel <span>1988</span>) and discouraging grazers (Wood et al. <span>2015</span>). The dead cells accumulating at the sediment surface provide additional substrate for microbial growth and respiration, promoting anoxia that releases additional nutrients from the sediment and organic matter (Fig. 1). The steep nutrient gradient between pore water and the overlying water column fosters more rapid movement of nutrients to attached algae, stimulating further growth. During the day, the top of the photosynthetic mat produces abundant oxygen that can be drawn downward across a relatively steep oxygen gradient toward respiring microbes. High pH associated with high oxygen of the photosynthesizing mat can discourage daytime P release from calcareous sediments (Dodds <span>2003</span>). However, at night when photosynthesis ceases, the mat can become hypoxic or anoxic, allowing further release of nutrients from the sediment into the overlying periphyton mat. This strong diel contrast in oxygen and the associated pH not only affects nutrient dynamics but also creates a hostile environment for some grazers (Wood et al. <span>2015</span>) that already may have difficulty consuming the types of filamentous algae that sometimes dominate these blooms (Rosenberger et al. <span>2008</span>). Thus, the periphyton mat is positioned to both take advantage of internal nutrient release and potentially to benefit from reduced grazing pressure, altogether generating favorable conditions for its continued growth.</p><p>Where does this self-reinforcing cycle end? Some have noted that winter temperature and light reductions, as well as wave exposure, can dislodge periphyton mats when dead matter at the base of the mat reduces its stability (Vadeboncoeur et al. <span>2021</span>). In mountain lakes, a spring freshet after a high-snowpack winter can effectively scour material and flush it downstream, such that spring periphyton may have to become established on relatively bare substrate. If not, it is possible that a periphyton mat may persist through the winter or, under snow and ice, die back while still attached, encouraging hypoxia.</p><p>We have demonstrated in principle that microbially mediated nutrient release in tandem with the physical constraints of temperature-dependent oxygen saturation may be a ubiquitous mechanism for driving nearshore benthic algal blooms in clear lakes that are warming, but the data necessary to test this hypothesis are lacking. Limnology has focused on offshore water column dynamics, infrequently including nearshore or benthic measurements, much less those across the varied substrates of littoral zones (Vadeboncoeur et al. <span>2021</span>; Atkins et al. <span>2022</span>). Where data exist, we see that clear mountain lakes can exhibit higher temperatures nearshore, relative to offshore water, but temperature and oxygen measurements that include the sediment and the overlying water column are uncommon. Competing processes could drive water column oxygen nearshore in multiple directions (e.g., wind and waves increase it, daytime periphyton photosynthesis increases it, decomposition and still conditions with a thermal bar decrease it) so these data are clearly needed. In nearshore zones, we anticipate the benthos to be much warmer than the overlying water, as it is warmed not only by the overlying water mass but also by the heat of decomposition. Furthermore, the benthos is warmed by radiant heat from the sun that may be particularly strong at high elevation and particularly effective on darker substrate.</p><p>New research is needed at the sediment–water interface of lakes, to examine temperature and oxygen dynamics, as well as richer studies of nutrient flux and microbial dynamics. We have highlighted processes that may have contributed to the observations of periphyton blooms in relatively well-protected mountain lakes, but also recognize that these dynamics should be relevant for low-elevation lakes where increased periphyton blooms have been reported in recent decades. Warming temperatures, increasing levels of hypoxia, and associated changes in redox conditions may be occurring without detection in lakes where studies focus on the water column rather than the sediment–water interface. Such effects of warming on redox conditions are undoubtedly altering biogeochemistry at global scales, with implications not only for nutrient dynamics but also carbon cycles and pollutant release (Jane et al. <span>2021</span>).</p>","PeriodicalId":18128,"journal":{"name":"Limnology and Oceanography Letters","volume":null,"pages":null},"PeriodicalIF":5.1000,"publicationDate":"2023-10-31","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://onlinelibrary.wiley.com/doi/epdf/10.1002/lol2.10357","citationCount":"0","resultStr":null,"platform":"Semanticscholar","paperid":null,"PeriodicalName":"Limnology and Oceanography Letters","FirstCategoryId":"93","ListUrlMain":"https://onlinelibrary.wiley.com/doi/10.1002/lol2.10357","RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":null,"EPubDate":"","PubModel":"","JCR":"Q1","JCRName":"LIMNOLOGY","Score":null,"Total":0}
引用次数: 0

Abstract

Blooms of algae attached to the bottom of nearshore environments have increasingly been observed in clear, nutrient-poor lakes worldwide (Vadeboncoeur et al. 2021). The phenomenon is puzzling for at least two reasons. First, such nearshore benthic blooms appear to be common across heterogeneous contexts—from the world's largest lake in Siberia to small mountain lakes in the Rocky Mountains of North America. Second, the blooms are enigmatic because they have been observed in the near absence of direct human disturbances, such as those in well-protected, remote mountain lakes. A recent review (Vadeboncoeur et al. 2021) highlights the diversity of mechanisms through which these nearshore benthic blooms may be triggered—such as nutrient loading through atmospheric deposition or human activity within the watershed, changes in hydrodynamics associated with climate change, and food web alterations that reduce grazing pressure. Yet none of these potential drivers are common across the lakes where nearshore benthic algal blooms have been reported. Here, we suggest that a previously unappreciated driver is common across all lakes that experience warming associated with climate change—elevated nearshore temperatures that reduce oxygen and promote nutrient release from sediments under the biofilm. In principle, this phenomenon should be particularly notable in high-elevation lakes because water at higher elevation holds less oxygen at saturation, high-elevation lakes are warming more quickly than their lowland counterparts, and they can receive additional warming from relatively high solar radiation (Fig. 1). We briefly review the evidence in support of this concept, recognizing that the data necessary to rigorously test it do not yet exist; however, such data collection is feasible.

Algal taxa in oligotrophic systems are well adapted to naturally high-light and nutrient-poor conditions (Cantonati and Lowe 2014). Because nutrients at the sediment–water interface can be rapidly cycled, nutrient concentrations in the water column may not be reliable indicators of nutrient availability for benthic primary producers (Vadeboncoeur and Power 2017). Hot spots or hot moments of elevated nutrient concentrations in littoral regions favor green algae, leading to thick filamentous mats (also called filamentous algal blooms; Oleksy et al. 2021; Vadeboncoeur et al. 2021). These periphyton blooms appear to be an emergent response to changing environmental conditions in oligotrophic systems, yet the ultimate drivers behind their increased occurrence are debated and often obfuscated by confounding processes. For example, in Lake Baikal, increasing evidence has pointed to highly localized wastewater inputs leading to increased Ulothrix spp. and Spirogyra spp. abundance (Timoshkin et al. 2018; Meyer et al. 2022). Similarly, Lake Tahoe has experienced increased periphyton biomass likely due to a mix of wastewater-associated eutrophication, groundwater leachate, and complex physical and hydrological processes (Naranjo et al. 2019; Atkins et al. 2022). Although observations of increased periphyton blooms in lakes with adjacent human population can draw links between human activity and in-lake periphyton responses (e.g., Rosenberger et al. 2008), these blooms also appear to be increasing in remote, high-elevation systems that lack permanent human settlements (Oleksy et al. 2020).

High-elevation lakes located in mountainous regions are frequently characterized by low-nutrient concentrations, long periods of ice cover, high solar and UV radiation, as well as heterogeneous landscapes associated with complex topography (Moser et al. 2019). Despite their remote locations, historically oligotrophic high-elevation lakes have experienced primary productivity increases that sometimes have been attributed to global change, including atmospheric deposition of reactive nitrogen and phosphorus, species introductions, and climate change (Ballantyne et al. 2011; Saros et al. 2011; Catalan et al. 2013; Brahney et al. 2014; Sadro et al. 2018; Vadeboncoeur et al. 2021). Most of this literature describes changes to water column productivity. However, numerous studies have shown that the frequently neglected benthic habitats of oligotrophic lakes, including those at high elevations, dominate ecosystem processes of primary production and respiration (reviewed by Vadeboncoeur and Power 2017). Changes in benthic algal assemblages previously may have been overlooked. For instance, within lakes in the southern Rocky Mountains of North America, sediment records indicate that nearshore algal assemblages have changed appreciably in recent decades, with 200–300% increases in periphytic green algal species (Oleksy et al. 2020).

Although sources and magnitude of nutrient inputs vary greatly across lakes worldwide, a common factor is warming associated with climate change (O'Reilly et al. 2015), which can promote oxygen depletion (Jane et al. 2021). Mountainous regions are warming faster than adjacent low-lying areas (Pepin et al. 2022), and warm water holds less oxygen than cold water. In a high-elevation lake, relative to its lower elevation counterparts, the water column holds lower oxygen at saturation due to the inverse relationship between elevation (atmospheric pressure) and the oxygen capacity of water (Fig. 1). Hutchinson (1957) briefly alluded to the potential for this elevation–oxygen relationship to alter benthic ecology. The importance of not only oxygen content but also partial pressure is increasingly recognized as affecting biodiversity patterns among aquatic invertebrates (e.g., Verberk et al. 2011). Our mass balance calculation using a vertical 1D reaction–diffusion model suggests that elevation effects on oxygen in a warming mountain lake could account for sediment anoxia occurring days to weeks earlier than would occur in a warming lake at sea level (Supporting Information). High solar radiation in mountain lakes can contribute to additional warming, and nearshore temperatures can increase markedly relative to the offshore. In some cases, as nearshore temperatures warm, a thermal bar may develop, reducing mixing and allowing littoral water temperatures to become even warmer (Vadeboncoeur et al. 2021). Warming sediments can quickly stimulate heterotrophic microbial processes that consume oxygen (Bergström et al. 2010). Convective cooling in the littoral zones can further limit horizontal exchange of oxygen and nutrients with offshore waters (Doda et al. 2023). These combined factors could explain why mountain lake nearshore blooms have been so noticeable in the absence of other clear drivers.

Warming littoral zone temperatures can decrease oxygen available for aerobic metabolism, creating an environment more favorable to anaerobic metabolism just a few millimeters into the sediments (Fig. 1, Schlesinger and Bernhardt 2013), particularly at night when photosynthesis does not produce oxygen. Microbial consumption of oxygen in sediments frequently exceeds the oxygen supply through diffusion (Fenchel and Finlay 2008). Without oxygen, microbes cannot use oxidative phosphorylation to convert organic matter into CO2, and instead must rely on the alternate electron acceptors including nitrate ( NO 3 ), iron (Fe3+), manganese (Mn4+), and sulfate ( SO 4 2 ). These alternate electron acceptors are exploited sequentially based on their energetic favorability and produce electron donors including reduced bioavailable forms of carbon, nitrogen ( NH 4 + ), iron (Fe2+), and sulfur (H2S) that may diffuse into overlying oxygenated water (McClure et al. 2021). For example, nitrate and ammonium become bioavailable in locations where oxygen conditions fluctuate and allow temporal and spatial coupling of the anaerobic and aerobic metabolisms involved in nitrogen cycling (Davidson et al. 2000). In addition, oxygen-depleted water in the sediments can result in high phosphorus concentrations because ferric iron reduction (Fe3+ to Fe2+) coupled with slightly acidic pH conditions (particularly at night when photosynthesis ceases) releases bioavailable forms of phosphorus (Gotoh and Patrick 1974). Importantly, diurnal heating of sediments in the littoral zone can drive water movement within surficial sediments, creating convection of pore water that may further increase availability of bioavailable nutrients to periphyton (Axler and Reuter 1996).

Altogether, the fluctuations in oxygen availability and temperature in littoral zones can increase availability of nutrients released from sediment, where they are efficiently intercepted by periphyton (Carlton and Wetzel 1988; Dodds 2003) and may not become elevated in the water column (e.g., Rosenberger et al. 2008). Complex successional patterns, such as diatomaceous mucilage production can initiate an early, physical barrier between the water column and the sediments (Hoagland et al. 1982; Wood et al. 2015). As the biofilm undergoes colonization and succession, warm temperatures may accelerate heterotrophic processes, thereby promoting biofilm growth and further impeding exchange between the water column and sediment. Most importantly, nutrients released from the sediment are directly used by periphyton in the mat, and do not reach the water column; concurrently, the biofilm impedes movement of oxygen from the water column into the sediment, promoting anoxia which encourages nutrient release.

Once a robust biofilm is established, periphyton blooms can promote an environment that is favorable for their further growth—both by stimulating internal nutrient release (Carlton and Wetzel 1988) and discouraging grazers (Wood et al. 2015). The dead cells accumulating at the sediment surface provide additional substrate for microbial growth and respiration, promoting anoxia that releases additional nutrients from the sediment and organic matter (Fig. 1). The steep nutrient gradient between pore water and the overlying water column fosters more rapid movement of nutrients to attached algae, stimulating further growth. During the day, the top of the photosynthetic mat produces abundant oxygen that can be drawn downward across a relatively steep oxygen gradient toward respiring microbes. High pH associated with high oxygen of the photosynthesizing mat can discourage daytime P release from calcareous sediments (Dodds 2003). However, at night when photosynthesis ceases, the mat can become hypoxic or anoxic, allowing further release of nutrients from the sediment into the overlying periphyton mat. This strong diel contrast in oxygen and the associated pH not only affects nutrient dynamics but also creates a hostile environment for some grazers (Wood et al. 2015) that already may have difficulty consuming the types of filamentous algae that sometimes dominate these blooms (Rosenberger et al. 2008). Thus, the periphyton mat is positioned to both take advantage of internal nutrient release and potentially to benefit from reduced grazing pressure, altogether generating favorable conditions for its continued growth.

Where does this self-reinforcing cycle end? Some have noted that winter temperature and light reductions, as well as wave exposure, can dislodge periphyton mats when dead matter at the base of the mat reduces its stability (Vadeboncoeur et al. 2021). In mountain lakes, a spring freshet after a high-snowpack winter can effectively scour material and flush it downstream, such that spring periphyton may have to become established on relatively bare substrate. If not, it is possible that a periphyton mat may persist through the winter or, under snow and ice, die back while still attached, encouraging hypoxia.

We have demonstrated in principle that microbially mediated nutrient release in tandem with the physical constraints of temperature-dependent oxygen saturation may be a ubiquitous mechanism for driving nearshore benthic algal blooms in clear lakes that are warming, but the data necessary to test this hypothesis are lacking. Limnology has focused on offshore water column dynamics, infrequently including nearshore or benthic measurements, much less those across the varied substrates of littoral zones (Vadeboncoeur et al. 2021; Atkins et al. 2022). Where data exist, we see that clear mountain lakes can exhibit higher temperatures nearshore, relative to offshore water, but temperature and oxygen measurements that include the sediment and the overlying water column are uncommon. Competing processes could drive water column oxygen nearshore in multiple directions (e.g., wind and waves increase it, daytime periphyton photosynthesis increases it, decomposition and still conditions with a thermal bar decrease it) so these data are clearly needed. In nearshore zones, we anticipate the benthos to be much warmer than the overlying water, as it is warmed not only by the overlying water mass but also by the heat of decomposition. Furthermore, the benthos is warmed by radiant heat from the sun that may be particularly strong at high elevation and particularly effective on darker substrate.

New research is needed at the sediment–water interface of lakes, to examine temperature and oxygen dynamics, as well as richer studies of nutrient flux and microbial dynamics. We have highlighted processes that may have contributed to the observations of periphyton blooms in relatively well-protected mountain lakes, but also recognize that these dynamics should be relevant for low-elevation lakes where increased periphyton blooms have been reported in recent decades. Warming temperatures, increasing levels of hypoxia, and associated changes in redox conditions may be occurring without detection in lakes where studies focus on the water column rather than the sediment–water interface. Such effects of warming on redox conditions are undoubtedly altering biogeochemistry at global scales, with implications not only for nutrient dynamics but also carbon cycles and pollutant release (Jane et al. 2021).

Abstract Image

查看原文
分享 分享
微信好友 朋友圈 QQ好友 复制链接
本刊更多论文
气候变暖引起的底栖氧化还原变化是高海拔湖泊底栖藻类水华加剧的潜在驱动因素
在全世界清澈、营养贫乏的湖泊中,越来越多地观察到附着在近岸环境底部的藻类繁殖(Vadeboncoeur 等,2021 年)。这一现象令人费解,至少有两个原因。首先,这种近岸底栖生物藻华似乎在不同的环境中都很常见--从西伯利亚的世界最大湖泊到北美落基山的小山湖。其次,底栖动物水华之所以神秘,是因为它们是在几乎没有人类直接干扰的情况下被观测到的,例如在保护良好的偏远山区湖泊中。最近的一篇综述(Vadeboncoeur 等人,2021 年)强调了引发这些近岸底栖动物水华的机制的多样性--例如通过大气沉降或流域内的人类活动造成的营养负荷、与气候变化相关的水动力变化以及减少放牧压力的食物网改变。然而,在已报道近岸底栖藻类水华的湖泊中,这些潜在的驱动因素都不常见。在这里,我们提出了一个以前未被重视的驱动因素,它在所有因气候变化而变暖的湖泊中都很常见--近岸温度升高会减少氧气,促进生物膜下沉积物中营养物质的释放。原则上,这种现象在高海拔湖泊中应特别明显,因为海拔较高的水体所含的饱和氧气较少,高海拔湖泊比低洼湖泊升温更快,而且它们还能从相对较高的太阳辐射中获得额外的升温(图 1)。我们简要回顾了支持这一概念的证据,同时认识到严格检验这一概念所需的数据尚不存在;不过,收集此类数据是可行的。寡营养系统中的藻类类群非常适应自然的高光照和贫养分条件(Cantonati 和 Lowe,2014 年)。由于沉积物-水界面的营养物质可以快速循环,水体中的营养物质浓度可能不是底栖初级生产者营养物质可用性的可靠指标(Vadeboncoeur 和 Power,2017 年)。沿岸地区营养物质浓度升高的热点或热点时刻有利于绿藻生长,从而形成厚厚的丝状藻垫(也称为丝状藻华;Oleksy 等,2021 年;Vadeboncoeur 等,2021 年)。这些浮游植物藻华似乎是对寡营养系统中不断变化的环境条件的一种新反应,但其发生率增加背后的最终驱动因素还存在争议,而且往往被混杂的过程所混淆。例如,在贝加尔湖,越来越多的证据表明,高度局部化的废水输入导致 Ulothrix 属和 Spirogyra 属丰度增加(Timoshkin 等,2018 年;Meyer 等,2022 年)。同样,太浩湖也出现了浮游生物生物量增加的现象,这可能是由于与废水相关的富营养化、地下水渗滤液以及复杂的物理和水文过程共同作用的结果(Naranjo 等人,2019 年;Atkins 等人,2022 年)。尽管在有邻近人类居住的湖泊中观察到的围岩藻华增加现象可以将人类活动与湖泊中的围岩反应联系起来(例如,Rosenberger 等人,2008 年),但这并不意味着人类活动与湖泊中的围岩反应之间存在联系、位于山区的高海拔湖泊通常营养浓度低、冰覆盖时间长、太阳辐射和紫外线辐射强,而且地形复杂,地貌多变(Moser 等,2019 年)。尽管地处偏远,但历史上寡营养的高海拔湖泊经历了初级生产力的增长,有时这种增长可归因于全球变化,包括大气中活性氮和磷的沉积、物种引入以及气候变化(Ballantyne 等,2011 年;Saros 等,2011 年;Catalan 等,2013 年;Brahney 等,2014 年;Sadro 等,2018 年;Vadeboncoeur 等,2021 年)。这些文献大多描述了水体生产力的变化。然而,大量研究表明,寡营养湖泊(包括高海拔湖泊)中经常被忽视的底栖生境主导着生态系统的初级生产和呼吸过程(Vadeboncoeur 和 Power 2017 年的综述)。底栖藻类组合的变化以前可能被忽视。例如,在北美落基山脉南部的湖泊中,沉积物记录表明近岸藻类群在最近几十年发生了显著变化,附生绿藻物种增加了 200-300% (Oleksy 等,2020 年)。虽然世界各地湖泊的营养物质输入来源和规模差异很大,但一个共同因素是与气候变化相关的气候变暖(O'Reilly 等,2015 年),这会导致氧气耗竭(Jane 等,2021 年)。
本文章由计算机程序翻译,如有差异,请以英文原文为准。
求助全文
约1分钟内获得全文 去求助
来源期刊
CiteScore
10.00
自引率
3.80%
发文量
63
审稿时长
25 weeks
期刊介绍: Limnology and Oceanography Letters (LO-Letters) serves as a platform for communicating the latest innovative and trend-setting research in the aquatic sciences. Manuscripts submitted to LO-Letters are expected to present high-impact, cutting-edge results, discoveries, or conceptual developments across all areas of limnology and oceanography, including their integration. Selection criteria for manuscripts include their broad relevance to the field, strong empirical and conceptual foundations, succinct and elegant conclusions, and potential to advance knowledge in aquatic sciences.
期刊最新文献
Disentangling effects of droughts and heatwaves on alpine periphyton communities: A mesocosm experiment Snow removal cools a small dystrophic lake Unraveling Lake Geneva's hypoxia crisis in the Anthropocene Simple visualization of fish migration history based on high‐resolution otolith δ18O profiles and hydrodynamic models Arctic fishes reveal patterns in radiocarbon age across habitats and with recent climate change
×
引用
GB/T 7714-2015
复制
MLA
复制
APA
复制
导出至
BibTeX EndNote RefMan NoteFirst NoteExpress
×
×
提示
您的信息不完整,为了账户安全,请先补充。
现在去补充
×
提示
您因"违规操作"
具体请查看互助需知
我知道了
×
提示
现在去查看 取消
×
提示
确定
0
微信
客服QQ
Book学术公众号 扫码关注我们
反馈
×
意见反馈
请填写您的意见或建议
请填写您的手机或邮箱
已复制链接
已复制链接
快去分享给好友吧!
我知道了
×
扫码分享
扫码分享
Book学术官方微信
Book学术文献互助
Book学术文献互助群
群 号:481959085
Book学术
文献互助 智能选刊 最新文献 互助须知 联系我们:info@booksci.cn
Book学术提供免费学术资源搜索服务,方便国内外学者检索中英文文献。致力于提供最便捷和优质的服务体验。
Copyright © 2023 Book学术 All rights reserved.
ghs 京公网安备 11010802042870号 京ICP备2023020795号-1