Allochthonous Nutrient Inputs Research Articles

Arctic cyanobacterial mat community diversity decreases with latitude across the Canadian Arctic.

Cyanobacterial mats are commonly reported as hotspots of microbial diversity across polar environments. These thick, multilayered microbial communities provide a refuge from extreme environmental conditions, with many species able to grow and coexist despite the low allochthonous nutrient inputs. The visibly dominant phototrophic biomass is dependent on internal nutrient recycling by heterotrophic organisms within the mats; however, the specific contribution of heterotrophic protists remains little explored. In this study, mat community diversity was examined along a latitudinal gradient (55-83°N), spanning subarctic taiga, tundra, polar desert, and the High Arctic ice shelves. The prokaryotic and eukaryotic communities were targeted, respectively, by V4 16S ribosomal RNA (rRNA) and V9 18S rRNA gene amplicon high-throughput sequencing. Prokaryotic and eukaryotic richness decreased, in tandem with decreasing temperatures and shorter seasons of light availability, from the subarctic to the High Arctic. Taxonomy-based annotation of the protist community revealed diverse phototrophic, mixotrophic, and heterotrophic genera in all mat communities, with fewer parasitic taxa in High Arctic communities. Co-occurrence network analysis identified greater heterogeneity in eukaryotic than prokaryotic community structure among cyanobacterial mats across the Canadian Arctic. Our findings highlight the sensitivity of microbial eukaryotes to environmental gradients across northern high latitudes.

Functional Responses of Phytoplankton Assemblages to Watershed Land Use and Environmental Gradients

Watershed land-use changes have been identified as major threats to lake fauna, subsequently affecting ecosystem functioning. In this study, the functional-based approach was used to examine the effects of land use and environmental changes on phytoplankton communities in four selected lakes in Northeast China. We also identified the sensitive functional traits as indicators of environmental stressors. The integration of RLQ analysis with the fourth-corner approach significantly identified five of 18 functional trait categories, including flagella, filamentous, unicellular, mixotrophic, and chlorophyll c, as potential indicators to changes in watershed land-use intensity and environmental gradients. Significant relationships between traits and land use and water quality highlighted the consequential indirect impact of extensive agricultural and urban development on phytoplankton via allochthonous nutrient inputs and various contaminants. In addition, the functional richness of phytoplankton assemblages generally increased along with surface area and forests, but decreased along with intensive agricultural and urban land use, implying that functional homogenization may cause a reduction in ecosystem productivity and reliability to land-use intensity. Given the superior performance of the functional-based approach, our findings also highlighted the importance of the application of both the biological traits and functional diversity index in monitoring programs for lake ecosystems.

Quantifying seasonal succession of phytoplankton trait‐environment associations in human‐altered landscapes

AbstractIntegration of species traits in direct gradient analysis generates insights into how communities are assembled and may respond to environmental changes. We investigated phytoplankton trait‐environment relationships for over 300 taxa during the open‐water season across 75 north‐temperate lakes and reservoirs in Alberta, Canada. An innovative, data‐driven approach was applied using iterative model selection for RLQ optimization to reveal key monthly associations. Fourth‐corner analysis then tested the significance of relationships using spatially and phylogenetically constrained null models derived by Moran spectral randomization. Both local‐ and regional‐scale drivers of succession were found with evidence of deterministic filtering by traits increasing in mid‐summer. Trait associations to land‐use and water quality highlighted potential anthropogenic cross‐scale interactions, such as logging and pasture development affecting phytoplankton via allochthonous nutrient inputs. Biogeographic factors (e.g., elevation and habitat size) and associated temperature and chemical gradients (e.g., pH and bicarbonate) were also linked to multiple morphological, physiological, and behavioral traits, including potential toxin production. Several correlated traits emphasized importance of trait syndromes corresponding to distinct taxonomic groups (e.g., cyanobacteria and green algae). However, rather than clustering species with shared ecological preferences or roles, our study builds on past trait‐based approaches to phytoplankton by testing for explicit trait associations with a range of environmental factors. Thus, we provide a novel, quantitative means of revealing environmental constraints on communities and translating their compositional changes under climate and other human influences into functional impacts on freshwater ecosystems.

Do inferences about freshwater phytoplankton communities change when based on microscopy or high‐throughput sequencing data?

Abstract Microscopy and high‐throughput sequencing (HTS) detect and quantify algae differently. It is not known if microscopy‐based abundance or biomass better compare to HTS data or how methodological differences affect ecological inferences about the phytoplankton communities studied. We investigated methodological (abundancemicroscopy vs. abundanceHTS, biomassmicroscopy vs. abundanceHTS), habitat (littoral, pelagic, deep hypolimnion), and year (2014 vs. 2017) differences for phytoplankton communities of Lake Tovel (Italy) using ANOVA. Specifically, we tested the hypothesis that depending on comparing abundancemicroscopy or biomassmicroscopy to abundanceHTS different effects would be indicated; we called this the metric effect. Furthermore, using samples from 2014 to 2017, we investigated environment–community relationships by a redundancy analysis based on abundancemicroscopy, biomassmicroscopy, and abundanceHTS, and compared the results. Approximately 9 times more operational taxonomic units were reported with HTS (n2014 = 819, n2017 = 891) than algal taxa with microscopy (n2014 = 90, n2017 = 109) in 2014 and 2017. While microscopically assessed algal taxa were evenly distributed among phyla, the vast majority of operational taxonomic units were attributed to Chrysophyta (2014 = 54%, 2017 = 62%) and Bacillariophyta (2014 = 19%, 2017 = 17%). A metric effect for method differences was generally observed comparing abundancemicroscopy to abundanceHTS with Chlorophyta, Cryptophyta, and Dinophyta showing higher % abundance with microscopy while richness and Chrysophyta showed higher values with HTS. Almost no metric effects were found in 2014, but they were common across phyla in 2017. Bacillariophyta and Eustigmatophyta showed the same habitat differences when comparing biomassmicroscopy to abundanceHTS. Dinophyta showed habitat differences only with microscopy, while Chyrsophyta showed habitat differences only with HTS; these results were probably related to technical bias and strengths of HTS, respectively. Habitat differences of phyla were reasonably related to their ecological niche and linked to factors such as temperature and feeding preferences; furthermore, phyla often showed a significant 2014‐versus‐2017 year effect. The year 2014 was very wet while 2017 had a dry winter, and we attributed the patterns found to allochthonous nutrient input by rain and decreased turbulence. Redundancy analyses based on phytoplankton communities assessed with microscopy and HTS, respectively, equally indicated the importance of hydrology, nutrients, and temperature for phytoplankton communities and discriminated the littoral from the deep hypolimnion. However, variance explained was higher with HTS, and the pelagic was similar to the deep hypolimnion with microscopy but to the littoral with HTS. Despite the different strengths of microscopy and HTS for biodiversity assessment, both datasets outlined similar large‐scale patterns linked to strong environmental control of phytoplankton communities as they related to habitat and year differences. According to our hypothesis, metric effects were common; however, no general rule was found as to whether abundancemicroscopy or biomassmicroscopy should be compared to abundanceHTS. Notwithstanding metric effects, HTS‐based data provided similar and more detailed information than microscopy, supporting the promise of HTS becoming the tool of the future for biodiversity research.

The ice cover shapes the spatial and temporal characteristics of water quality in Hulun Lake during winter

Abstract Being the largest boreal steppe lake in Northeast China, Hulun Lake has been characterized by eutrophication induced by abnormally high organic matter. This work investigated therefore the physicochemical and water quality parameters of Hulun Lake, and that of the inflowing Crulen River and Orshen River through winter, to reveal the spatial and temporal characteristics of water quality without impact of algal bloom, atmospheric deposition, wind or allochthonous nutrient input. Results showed that the prevention of wind-induced sedimentary resuspension accompanied with the minimized volume of tributary inflows is supposed to predominate the eutrophication alleviation. The formation of ice cover had a slight concentrative effect on water ion content. However, ice cover resulted in an increasingly homogenous distribution of phosphorus and oxygen-depleting organic matter over the entire lake. The two headwater streams demonstrated limited impact on water quality in estuaries in winter without showing evident coordination in upstream water nutrient level. It is suggested that the prevention of wind disturbance by ice cover and the subsequently modified hydrodynamic and water ecological processes are the determinant factors on water quality in Hulun Lake during winter.

Local Ecosystem Uptake of Stocked Trout by Cambarus bartonii and the Relevance of Prior Exposure to Stocking

We assessed variation in feeding preference of Cambarus bartonii (Appalachian Brook Crayfish) for stocked Salmo trutta (Brown Trout) or wild Salvelinus fontinalis (Brook Trout) across 8 central Pennsylvania headwater streams with different recent exposures to trout stocking. In separate trials, we allowed crayfish to interact with and choose between fillets of stocked Brown Trout or wild Brook Trout in either a flowing Y-apparatus or a standing-water aquarium. In the Y-apparatus trials and standing water aquarium trials, crayfish exhibited no detectable feeding preference based on proximity to stocking sites from which they were collected. In the Y-apparatus trials, crayfish were more likely to move towards a fillet type than not. Overall, our results provide evidence that crayfish do not distinguish between stocked Brown Trout and wild Brook Trout as food sources, and history of exposure to stocked trout does not influence feeding preference. Specifically, crayfish accept stocked trout as a food source, even if this resource is new to the environment (i.e., with the additions of new stocking sites in previously unstocked streams). Acceptance of stocked trout as a food resource suggests crayfish may play an important role in the local incorporation of this significant allochthonous nutrient input. Future research should address if local uptake of stocked trout by crayfish is able to mitigate downstream nutrient loads related to stocking.

Diatom bloom in the Amba River, west coast of India: A nutrient-enriched tropical river-fed estuary

The role of allochthonous nutrient inputs in governing phytoplankton distribution and abundance were assessed from the estuarine regions of the Amba River, west coast of India. A total of 35 species belonging to 24 genera were recorded, where the diatom Coscinodiscus oculus-iridis (99%) dominated the estuarine mouth with a density of 3.5 × 105 cells l−1. Community analyses indicate that diversity (H’) decreased towards the estuarine mouth (0.002 ± 0.001) compared to the middle (0.38 ± 0.06) and inner estuary (1.83 ± 0.14) due to the diatom outbreak. Chlorophyll a reached an average of 12.51 μg l−1 at the estuarine mouth, which is over three times the value determined in the middle estuary (4.25 μg l−1). The key sources of these land-based nutrients are identified as agricultural land and urban runoff for nitrogen (N) and phosphorus (P), extensive sand mining for silica (Si) and aeolian deposition of iron minerals from industrial conveyor belts. A linear correlation between cell density and chlorophyll a with chemical variables indicated that silicate coupled with excess nitrogen input was crucial causative factors for the bloom. The nutrient enrichment towards the estuarine mouth is due to the dispersal of these land derived nutrients by complex hydrological forces.

Spatial and temporal dynamics of pCO2 and CO2 flux in tropical Lake Malawi

AbstractNumerous studies have documented CO2 dynamics in temperate lakes, but few such studies have been conducted on tropical lakes. Spatial and seasonal variation of air and water pCO2, along with supporting limnological and meteorological variables, were measured aboard a vessel of opportunity along the north–south axis of Lake Malawi. These measurements were used to estimate annual net lake‐atmosphere CO2 flux and infer mechanisms regulating it. Surface pCO2 and CO2 flux varied significantly with season and location. Temporally, the lake was CO2‐undersaturated during the rainy season and the mixing season, and supersaturated at the onset of the mixing season and during the hot, stratified season. Concurrent measurements of lake temperature, weather conditions, phytoplankton biomass, and seston δ13C suggest that periods of net CO2 flux into the lake correspond with higher phytoplankton growth rates resulting from internal nutrient loading in the mixing season and allochthonous nutrient inputs in the rainy season. Unlike the rest of the lake, the southernmost region of the lake was usually CO2 supersaturated even though phytoplankton productivity is highest in this region. While the upwelling of hypolimnetic water at the southern end of the lake is a major source of nutrients that drive phytoplankton photosynthesis and CO2 uptake, the CO2 introduced in upwelled water appears to overwhelm photosynthetic capacity locally, especially at the onset of the mixing season. Lake Malawi appears to be a net CO2 sink with an annual whole‐lake CO2 flux of −2.17 ± 0.25 × 1010 mol C yr−1 and a mean daily CO2 flux of −2.05 ± 0.27 mmol C m−2 d−1. A comparison of deep‐water C : P ratios with epilimnetic seston C : P ratios suggests that P is recycled more efficiently than C in the lake's anoxic hypolimnion, and so P vertical mixing creates a carbon deficit that is met by flux from the atmosphere into the lake.

Influence of hydrology on water quality and trophic state of irrigation reservoirs in Sri Lanka

AbstractMany reservoirs provide multiple benefits to people around the world, in addition to primary uses such as irrigation. Thus, reservoir management should address their multiple uses. The water quality of ten irrigation reservoirs in Sri Lanka was examined in the present study with the objective of better understanding the effects of hydrological regimes on reservoir water quality and trophic state. Basic limnological parameters pertinent to the nutrient loads to, and trophic state of, the reservoirs were collected from June 2013 to February 2016. The sampling period was arbitrarily divided into two periods of approximately similar duration (period 1 = June 2013–September 2014; period 2 = October 2014–February 2016) to investigate whether or not there was a seasonal variation in the water quality parameters. Although temporal and spatial variations were observed, most water quality parameters were within the levels acceptable for drinking water standards. The 10 reservoirs were also ordinated by principal component analysis (PCA) on the basis of the water quality parameters of the two sampling periods in a two‐dimensional score plot. Reservoirs in the first principal component (PC1) axis were represented by negative scores attributable to the dissolved oxygen concentration and pH and, to a lesser extent, by electrical conductivity and chlorophyll‐a concentration. Positive scores in PC1 were represented by reservoirs with a score loading attributable to alkalinity, nitrate concentration, Secchi depth, temperature and seston weight and, to a lesser extent, from the total phosphorus concentration. There was a significant negative correlation of PC1 scores with relative reservoir water‐level fluctuation (RRLF; the ratio of mean reservoir water‐level amplitude to mean reservoir depth). Furthermore, Carlson's trophic index also were influenced by RRLF, although not by hydraulic retention time (HRT), indicating allochthonous nutrient inputs into the irrigation reservoirs were mainly governed by RRLF, but not by HRT. Thus, the results of the present study provide useful insights into achieving desirable reservoir water quality through the manipulation of the hydrological regime.

Diatom-inferred ecological responses of an oceanic lake system to volcanism and anthropogenic perturbations since 1290 CE

The impacts of natural- and human-induced processes on lake ecosystems in remote oceanic islands remain to be fully elucidated. These lakes are excellent candidates to analyze the importance of anthropogenic vs. natural forces driving lacustrine long-term ecological evolution from previous pristine pre-colonized conditions. Disentangling the effects of both is particularly relevant in highly active volcanic areas, where catastrophic eruptions can act as an atypical natural driver altering the lake's long-term ecological trajectories. In this paper we study past ecological changes occurring in Lake Azul (São Miguel island), a crater lake from the remote Azorean archipelago, to address which were the main causes of its long-term trophic history. We analyzed diatom assemblages, sedimentology, and bulk organic matter of sediments deposited since ca. 1290 CE, when a huge local eruption occurred. This episode drove the evolution of Lake Azul through six distinct phases, commencing with a restart of ecological succession after tephra deposition disrupted biogeochemical cycling. The alteration was so profound that the lake underwent a state of oligotrophic conditions for approx. 650 yr. Nutrients were sourced by fish-induced internal recycling and the overflow of the near Lake Verde during this period, rather than by allochthonous nutrient inputs modulated by climate variability and/or vegetation cover changes in the watershed after the official Portuguese colonization. It was only after recent artificial fertilization when the system overcame the volcanic-induced long-term resilience. This over-fertilization and a reduction in water turnover exacerbated the recent symptoms of eutrophication after 1990 CE. Contrary to other studies, Lake Azul constitutes an uncommon case of long-term resilience to trophic change induced by a cataclysmic volcanic eruption. It brings new insights into the fate of lake ecosystems which might be affected by similar events in the future.

Turbulence measurements suggest high rates of new production over the shelf edge in the northeastern North Sea during summer

Abstract. New production, i.e. that driven by allochthonous nutrient inputs, is the only form of primary production that can lead to net increases in organic material and is, therefore, important for understanding energy flow in marine ecosystems. The spatial distribution of new production is generally, however, not well known. Using data collected in July 2016, we analyse the potential for vertical mixing to support new production in the upper layers of the northeastern portion of the North Sea. Relatively large (up to >0.5 mmol N m−2 d−1) nitrate fluxes due to turbulent vertical mixing into the euphotic zone were found at some stations over the shelf edge, while low values (< 0.1 mmol N m−2 d−1) were found in the deeper open area north of the shelf edge. The low vertical mixing rates (dissipation rates of turbulent kinetic energy below 10−8 W kg−1, corresponding to vertical turbulent diffusion coefficients of 10−6–10−5 m2 s−1) implied f ratios of <0.02 in the open waters north of the shelf edge. In the shallow (<50 m) southern and central part of the study area, inorganic nutrients were low and nitrate undetectable, suggesting negligible new production here, despite relatively high concentrations of chlorophyll a being found in the bottom layer. Thus, high rates of new production seem to be concentrated around the shelf-edge zone and in association with localized features exhibiting enhanced vertical mixing. We find that the nutricline depth is significantly deeper at the shelf edge and interference with increased mixing in this deeper depth range can explain the increased diapycnal nitrate fluxes. Overall, this suggests that the shelf-edge zone may be the major nutrient supplier to the euphotic zone in this area during the period of summer stratification.

Tracking the Limnoecological History of Lake Hiidenvesi (Southern Finland) Using the Paleolimnological Approach

We examined a sediment record from Lake Hiidenvesi in southern Finland using paleolimnological methods to trace its limnoecological history. In our record, beginning from the 1940s, chironomid (Diptera) assemblages shifted from typical boreal taxa towards mesotrophic community assemblages at ~ 1960–1980 CE being finally replaced by eutrophic taxa from the 1990s onward. The diatom (Bacillariophyceae) assemblages reflected relatively nutrient rich conditions throughout the record showing a further increase in eutrophic taxa from the 1970s onward. A chironomid-based reconstruction of late-winter hypolimnetic dissolved oxygen (DO) conditions suggested anoxic conditions already in the 1950s, probably reflecting increased inlake production due to allochthonous nutrient inputs and related increase in biological oxygen consumption. However, the reconstruction also indicated large variability in long-term oxygen conditions that appear typical for the basin. With regard to nutrient status, chironomid- and diatom-based reconstructions of total phosphorus (TP) showed a similar trend throughout the record, although, chironomids indicated a more straightforward eutrophication process in the benthic habitat and seemed to reflect the intensified human activities in the catchment more strongly than diatoms. The DO and TP reconstructions were mostly similar in trends compared to the measured data available since the 1970s/1980s. However, the increase in TP during the most recent years in both reconstructions was not visible in the monitored data. The results of our multiproxy study emphasize the significance of including both epilimnetic and hypolimnetic systems in water quality assessments and provide important long-term limnoecological information that will be useful in the future when setting targets for restoration.

Longitudinal variation of benthic macroinvertebrate communities in two contrasting tropical streams in Sri Lanka

The benthic macroinvertebrate fauna and main abiotic parameters were studied to understand the patterns of diversity and structure along the temporal and longitudinal gradients in two tropical lotic ecosystems in the wet and dry zones of Sri Lanka. Invertebrate abundance (annual means) was in the same magnitude in the two streams (2,520 ind. m−2 in the wet zone stream and 2,940 ind. m−2 in the dry zone stream). Both streams had similar annual mean diversity levels measured as Shannon diversity (Eswathu Oya (wet zone) = 2.11; Yan Oya (dry zone) = 2.07), with a mean annual evenness (Pielou evenness) of 0.56 ± 0.14 for Eswathu Oya and 0.60 ± 0.09 for Yan Oya. Along the longitudinal gradient, abundance and taxa richness increased toward the lower reaches in the wet zone stream but decreased in the dry zone stream. Composition of functional feeding groups was greatly influenced by abiotic factors in the temporal gradient than in the longitudinal gradient. This was possibly due to the seasonal patterns of flow regimes, and allochthonous nutrient inputs into the streams. Hence, resource management and conservation as well as attempts of ecological assessment in tropical streams should be based not only on the in‐stream characteristics but also on the catchment properties.

Seasonal distribution of phytoplankton and its association with physico-chemical parameters in coastal waters of Malvan, west coast of India.

Malvan coast is one of the Marine Protected Area (MPA) of Maharashtra because of its rich coral reef and biodiversity. The study investigated on phytoplankton assemblage and their diversity with respect to physico-chemical parameters covering protected and unprotected area of Malvan coast. Physico-chemical parameters such as salinity, nitrite, nitrate, and ammonia did not display seasonality due to inadequate fresh water influx and allochthonous nutrient input. Positive correlation of phosphate (r=0.96, p<0.0001) and silicate (r=0.91, p<0.0001) with Total Suspended Solids (TSS) confirmed their autochthonous origin as a result of resuspension of bottom sediments during monsoon. A total of 57 phytoplankton species were identified mostly dominated by Bascillariophyceae (40 species), followed by Dinophyceae (9 species), Chlorophyceae (5 species), Cyanophyceae (2 species), and Dictyochophyceae (1 species) from Malvan coast. Canonical correspondence analysis (CCA) revealed that water temperature and TSS were the most significant parameters influencing the distribution and seasonal shift in phytoplankton species such as Skeletonema costatum and Chaetoceros sp. during pre-monsoon and Psedo-nitzschia sp., Streptotheca thamensis, Eucampia zodiacus, and Lithodesmium undulatum during post-monsoon. Silicate and phosphate had minor influence on phytoplankton distribution. Shannon-Wiener diversity index as a pollution index suggested that the study area was incipiently polluted except at bay stations. Despite of various human interventions the water quality and phytoplankton assemblage of this area has not reached to an alarming situation. The current study provides a valuable baseline data on phytoplankton assemblage from Malvan coast.

Sources and controls of organic carbon in lakes across the subarctic treeline

Abundant northern lakes have an intrinsic role in the transport, sequestration, and mineralization of terrestrial organic carbon. The quantity and quality of this carbon control vital aquatic biogeochemical processes, and influence the metabolic balance of lakes with subsequent impact on the global carbon cycle. We measured concentrations and type of dissolved organic matter and elemental and stable isotopic composition of carbon and nitrogen in 31 subarctic lakes with varying catchment types across the treeline in northern Finland, integrating both the pelagic (lake water) and the benthic (surface sediments) carbon pools for a comprehensive understanding of landscape influence on aquatic carbon dynamics. Wetland cover was identified as the primary catchment control over the aquatic carbon pools, reflected particularly in the bio-optical properties of lake water. Landscape influence on sediment carbon content and composition, mirroring largely the structure and productivity of the aquatic communities, was primarily connected to allochthonous nutrient inputs fueling autotrophic production. Basin depth and benthic production were identified as important internal controls on the surface sediment geochemistry. Overall, our results suggest that shallow subarctic lakes will be particularly susceptible to climate-mediated changes in the export of terrestrial organic matter from wetlands. Whether the landscape influence will promote the channeling of terrestrial carbon into the atmosphere via aquatic ecosystems will strongly depend on the interplay between the biogeochemical characteristic of the allochthonous carbon inputs, terrestrial nutrient fluxes, and the depth of the recipient ecosystems.

Heterotrophic bacteria in Antarctic lacustrine and glacial environments

Antarctica has the greatest diversity of lakes types on the planet including freshwater, brackish, saline and hypersaline systems, epishelf lakes, ice shelf lakes and lakes and cryoconite holes on glacier surfaces. Beneath the continental ice sheet, there are hundreds of subglacial lakes. These systems are dominated by microbial food webs, with few or no metazoans. They are subject to continuous cold, low annual levels of photosynthetically active radiation and little or no allochthonous nutrient inputs from their catchments. Subglacial lakes function in darkness. Heterotrophic bacteria are a conspicuous and important component of the simple truncated food webs present. Bacterial abundance and production vary between freshwater and saline lakes, the latter being more productive. The bacterioplankton functions throughout the year, even in the darkness of winter when primary production is curtailed. In more extreme glacial habitats, biomass is even lower with low rates of production during the annual melt season. Inter-annual variation appears to be a characteristic of bacterial production in lakes. The factors that control production appear to be phosphorus limitation and grazing by heterotrophic and mixotrophic flagellate protozoa. The evidence suggests high rates of viral infection in bacteria and consequent viral lysis, resulting in significant carbon recycling, which undoubtedly supports bacterial growth in winter. The biodiversity of lacustrine Antarctic heterotrophic bacteria is still relatively poorly researched. However, most of the main phyla are represented and some patterns are beginning to emerge. One of the major problems is that data for heterotrophic bacteria are confined to a few regions served by well-resourced research stations, such as the McMurdo Dry Valleys, the Vestfold Hills and Signy Island. A more holistic multidisciplinary approach is needed to provide a detailed understanding of the functioning, biodiversity and evolution of these communities. This is particularly important as Antarctic lakes are regarded as sentinels of climate change.

“Ornithological eutrophication” as a source of allochthonous nutrient enrichment in Anavilundawa reservoir, Sri Lanka

Mass aggregation of waterfowls for breeding, results in allochthonous nutrient inputs into aquatic systems. This study evaluated accumulation of bird droppings as allochthonus nutrient input and its fluctuations in Anavilundawa International Ramsar Sanctuary in Sri Lanka where Asian openbill (Anastomus oscitans) mass breeding occurs annually. Reservoir was divided into four strata: Inlet, breeding ground, reservoir centre and outlet. The highest nutrients levels (NO3−, PO43−, NH4+, alkalinity) and the lowest dissolved oxygen and pH levels were recorded in breeding grounds for both surface and bottom water. The highest turbidity was recorded in inlet surface and centre bottom water. Canonical Variate Analysis of water quality parameters indicated the significantly distinct influence of ornithological eutrophication on surface water of four strata whilst, showing similarities in water quality of bottom layers in inlet and outlet. In the breeding ground, surface water was covered with thick mats of aquatic flora consisting of Water hyacinth, Salvinia, duckweed and Polygonum. Therefore, it is concluded that in addition to dilution, amelioration of water quality could also be happening due to absorption by plants. Due to interactions between invasive plants and waterfowls, restoration with native aquatic flora is needed to be considered to regain reservoir resilience and self-sustenance.

Climatic and lacustrine morphometric controls of diatom paleoproductivity in a tropical Andean lake

The coupling of lake dynamics with catchment biogeochemistry is considered the key element controlling primary production in mountain lakes at time scales of a few decades to millennia, yet little is known on the impacts of the morphometry of lakes throughout their ontogeny. As Lake Chungará (Central Andean Altiplano, northern Chile) experienced long-term lake-level fluctuations that strongly modified its area:volume ratio, it is an ideal system for exploring the relative roles that long-term climatic shifts and lake morphometry play on biosiliceous lacustrine productivity. In this paper, we review previous data on the percent contents of total organic carbon, total inorganic carbon, total nitrogen, total biogenic silica, isotopic composition of organic matter, carbonates, and diatom frustules, as well as data on the abundance of the chlorophycean Botryococcus braunii in this lake for the period 12,400–1300 cal yr BP. We also include new data on organic carbon and biogenic silica mass accumulation rates and the diatom assemblage composition of an offshore core dated using 14C and U/Th.Biosiliceous productivity in Lake Chungará was influenced by shifts in allochthonous nutrient inputs related to variability in precipitation. Humid phases dated at approx. 12,400 to 10,000 and 9600 to 7400 cal yr BP coincide with periods of elevated productivity, whereas decreases in productivity were recorded during arid phases dated at approx. 10,000 to 9600 and 7400 to 3550 cal yr BP (Andean mid-Holocene Aridity Period). However, morphometry-related in–lake controls led to a lack of a linear response of productivity to precipitation variability. During the late Glacial to early Holocene, lowstands facilitated complete water column mixing, prompting episodic massive blooms of a large centric diatom, Cyclostephanos cf. andinus. Thus, moderate productivity could be maintained, regardless of aridity, by this phenomenon of morphometric eutrophy during the early history of the lake. The subsequent net increase in lake level introduced modifications in the area of the epilimnion sediments versus the total volume of the epilimnion, preventing complete overturn. Surpassing a certain depth threshold at approx. 8300 cal yr BP caused cessation of the morphometric eutrophy conditions associated with Cyclostephanos cf. andinus superblooms. After 7300 cal yr BP, the lake experienced a decrease in biosiliceous productivity and a change of state that involved a stronger dependence on precipitation variability, with a lesser contribution of diatoms to the total primary productivity. Our results show that the interpretation of lacustrine paleoproductivity records as paleoclimatic archives needs to take into account the effects of changes in the epilimnion sediment area to epilimnion volume ratio in association with lake ontogeny.

Responses of Narrowleaf Cattail (Typha angustifolia) to Combinations of Salinity and Nutrient Additions: Implications for Coastal Marsh Restoration

Narrowleaf cattail ( Typha angustifolia ) is an exotic, invasive species in North America that has become abundant in many tidally-restricted salt marshes. Restoration of tidal flow to these wetlands results in elevated salinities that should favor the establishment of native salt marsh halophytes while reducing the abundance of narrowleaf cattail. However, there is some uncertainty about the salinity tolerance of narrowleaf cattail, which makes it difficult to predict vegetation trends and to interpret the actual results of restoration. Moreover, the effect of soil nutrient status on salinity tolerance of this species is virtually unknown, although many restoration projects occur in heavily urbanized settings with substantial allochthonous nutrient inputs. In this study, a salinity and nutrient addition experiment was conducted in a greenhouse to determine the effect of mineral nutrition on salinity responses in narrowleaf cattail. Within high salinity (~ 32 ppt) treatments, nutrients enhanced final biomass. Within the intermediate salinity (~ 17 ppt) treatments, nutrients significantly increased the number of leaves per shoot, sum of all leaf lengths, and final biomass. Under low salinity (~ 6 ppt) conditions, nutrient addition increased the mean height of the tallest shoot, mean height of all leaves, sum of all leaf lengths, and final biomass. The salinity responses and observed reductions in salinity-induced physiological stress by nutrient addition provide some context for forecasting and analyzing vegetation change in response to tidal restoration.

Retention and fate of groundwater-borne nitrogen in a coastal bay (Kinvara Bay, Western Ireland) during summer

The magnitude of submarine groundwater discharge (SGD) and its contribution to nitrogen biogeochemistry in a small embayment in the Western Coast of Ireland subject to occasional hypoxia were investigated during summer. Time series (24 h) of 222Rn, NO3−, NO2−, NH4+, dissolved reactive silicate (DRSi) and salinity (June 2010, July and September 2011 and July 2013), total dissolved phosphorus (TDP) (September 2011 and July 2013) and dissolved organic nitrogen (DON) (July 2013) were measured at the mouth of the bay and coupled with relevant sediment–water fluxes and input loadings to derive nutrient budgets. In-situ activity ratios of the naturally occurring radium isotopes 224Ra and 223Ra were employed in parallel to the freshwater fraction method to determine the timescale of freshwater retention in the system. Based on 222Rn mass balances (n = 4), the mean groundwater (±SE) discharge into Kinvara Bay was 10.4 ± 6.3×104 m3 days−1, delivering average loads of 376 ± 67 kg Si day−1 (as DRSi), 1.6 ± 0.2 kg P day−1 (as TDP) and ~280 kg N day−1 of dissolved nitrogen (272 ± 49 DIN, essentially as NO3−, and 8.2 ± 1.6 DON), which correspond to ~98.8, 49.1 and ~93.5 % of total allochthonous nutrient inputs respectively. Expressed on an areal basis and annual scale the exogenous N summer loading of Kinvara is equivalent to 25.9 g N m−2 year−1. Our biogeochemical budgets indicate that tight benthic-pelagic coupling contributes to the very high retention levels of N within the bay with subtidal sediments acting as a link in the internal N cycle via DNRA, while ~18 % of the exogenous N load is removed by benthic denitrification. Rapid cycling of DON into bioavailable forms of N within the timescale of freshwater retention in the system (~7 days) contributes ~50 % to local biological N fixation. Nutrient availability ratios are N:P ~173 and Si:P ~503, indicating that primary production is P-limited while the carbon yield (~3.01 × 105 mol C day−1, or ~0.313 kg C m−2 year−1) suggests the bay is eutrophic during the summer. SGD-borne Nitrogen loading is therefore the major driver of eutrophication in Kinvara Bay. Our biogeochemical characterization is consistent with the observed phytoplankton community composition and species succession and justifies the local observation of HAB’s. In addition, the relative magnitude of DNRA-promoted N retention compared to N removal by denitrification, coupled with seasonal hypoxia, suggests that the system is advanced in the chronological sequence of eutrophication effects on shallow coastal systems.