Water Nutrient Research Articles

Estimating nutrient stoichiometry and cascading influences on plankton in thermokarst lakes on the Qinghai-Tibet Plateau

Thermokarst lakes play a critical role in global biogeochemistry. Here we delved into nutrient stoichiometry and its cascading effects on plankton communities across thermokarst lakes on the Qinghai-Tibet Plateau. Our findings revealed significant variability in nutrient concentrations and stoichiometric ratios in both water and seston, indicating heterogeneous nature of thermokarst lakes. Phytoplankton communities were dominated by cyanobacteria. Zooplankton communities, though simple, varied significantly and responded distinctly to the prevailing nutrient stoichiometry, and particularly shown competitive interactions between copepods and Cladocera. Structural Equation Modeling revealed a complex web of interactions, underscoring the bottom-up influences from nutrient stoichiometry in water to phytoplankton/seston, and finally to zooplankton, although there were no direct relationships between phytoplankton and zooplankton communities. Water nutrient stoichiometry positively affected eukaryotic algae but negatively impacted seston stoichiometry, which. had a negative influence on copepods. Our study highlighted the intertwined relationships between nutrient stoichiometry and plankton communities within thermokarst lakes.

An assessment of N, P, Fe, Zn, Ni and Mo limitation on suspended nutrient diffusing substrates in nearshore areas of Lake Michigan and Lake Erie

In large lakes, metal availability sometimes limits the acquisition of nutrients (nitrogen, N and phosphorus, P) in offshore waters that are relatively isolated from tributaries and sediments. We hypothesize that metals may also be important within harmful algal blooms (HABs). HABs occur where nutrient loads are elevated, but bioassays often indicate that phytoplankton in HABs are N or P limited. Nutrient limitation may be exacerbated by corresponding limitations in several metals (i.e. nickel - Ni, molybdenum - Mo, zinc - Zn, and iron - Fe) that facilitate uptake and transformation of oxidized and organic forms of nutrients, such as urea, nitrate and organic phosphorus. The cyanotoxin microcystin has been hypothesized to have a role in metal management, so metal demand may also influence the toxicity of HABs. Here, we used nutrient diffusing substrates to measure how N, P, Ni, Mo, Zn and Fe amendments influenced the growth and toxicity of periphyton. Periphyton was grown suspended in 10 nearshore sites in Lake Michigan and Lake Erie (5 with and 5 without perennial HABs). Outside of blooms, we found no evidence for metal limitation or co-limitation. However, evidence for metal co-limitation was observed in two HABs sites (Zn in Green Bay and Zn, Mo, Ni and Fe in Sandusky Bay). N, P and Zn amendments all stimulated microcystin content in Maumee Bay. These data indicate that nutrient limitation occurs even within blooms, and the availability of metals may have an influence on growth, community composition and toxicity.

Characteristics of surface microlayer film under different freshwater environments: Physical, chemical, and biological properties

The surface microlayer film (SMF) has been observed worldwide in water environments and its environmental behavior plays a vital role in the migration and transformation of water pollutants. However, there has been little description and explanation of their characteristics in freshwater environments. Here, we investigate the characteristics of SMF under different freshwater trophic status. The results demonstrated that under sufficient nutrition, the interior characteristics of the SMF are densely arranged Fe3O4 skeletal structures, and the enrichment concentration of Fe3+ on the SMF reached 4.66 μg/mL, the dominant bacteria is Zoogloea. Under the constraint of nitrogen, the interior characteristics of the SMF is a tightly spherical encapsulated organic matter, the maximum enrichment concentration of Fe3+ on the SMF was only 0.75 μg/mL, Limnobacter and Acidocella are the dominant bacteria in the carbon and nitrogen constraint. Under iron constraint, the interior of the SMF is an entangled organic organism, and the coverage rate of the SMF was only 31.41 %, which decreased by 20.55 % and 8.58 %, compared with carbon and nitrogen constraint respectively, and the main microbial species is Cloacibacterium. These results reveal a strong correlation between water nutrient types and the formation of SMF, and established a connection between water pollution and SMF characteristics, provided a new approach for predicting water types using water surface microlayers, and have important implications for managing freshwater ecosystems.

How to effectively reduce sloping farmland nutrient loss and soil erosions in the Three Gorges Reservoir area

Fertilization and soil conservation measures play crucial roles in influencing nutrient loss and soil erosion on sloping farmlands. However, the long-term effects of these measures and the characterization of nutrient loss and sediment yield under different rainfall types and crop growth stages were not well studied. Therefore, we designed six treatments for sloping farmlands in the Three Gorges Reservoir Area with a field experiment. A field experiment included downslope cultivation with chemical fertilizer (DF), downslope cultivation with chemical fertilizer plus manure (DFM), cross-slope cultivation with chemical fertilizer plus manure (CFM), no-till straw cover with chemical fertilizer plus manure (NSFM), ridge plant hedges with chemical fertilizer plus manure (RFM), and biochar interception ditches with chemical fertilizer plus manure (BFM). The results indicated that soil and water conservation measures in association with manure substitution significantly reduced runoff depth (14.3–22.5 %), sediment yield (10.3–46.5 %), and total nitrogen (TN) loss (13.5–36.5 %) compared to DF. NSFM significantly reduced total phosphorus (TP) loss by 17.4 % and the TP loss from the other treatments did not show significant differences compared to DF. Rainfall intensity and runoff depth were identified as critical factors influencing nutrient loss and soil erosion. NSFM showed maximal nutrient reduction performance under different rainfall intensities, while DFM was not significantly effective. NO3--N and particulate P dominated the loss of TN and TP. The first 30 minutes of runoff generation and the seedling stage were identified as risk periods for N and P loss. The study suggests that the NSFM treatment was the appropriate method to prevent soil and water nutrient loss. This provides important insights for the precise control of nutrient loss and soil erosion on sloping farmlands.

Nutrient regeneration patterns for initiating and maintaining algae blooms-a case study of in Lake Taihu

In order to clarify the nitrogen (N) and phosphorus (P) regeneration patterns and internal mechanism for initiating and maintaining algal blooms in Lake Taihu, samples (including surface water and sediment) from 8 sites in Lake Taihu were collected for nine times from May 2010 to April 2011, and analyzed for total and labile organic matter, P fractionation and sorption behaviors, extracellular enzymatic activities (EEA), dehydrogenase activity, the respiratory electron transport system activity, and iron in sediment, EEA, N and P species and chlorophyll a (Chl. a) in surface water, as well as N and P species in interstitial water. In Lake Taihu, although severe blooms occurred in both Meiliang Bay and Zhushan Bay, the nutrient regeneration patterns stimulating the initiation and maintenance of algae blooms in these two bays were different. In Zhushan Bay with low EEA in surface water, abundant N and P flux from sediments, due to the degradation of organic matter and enzymatic hydrolysis in sediment, further stimulated the initiation and maintenance of algae blooms. In Meiliang Bay, in spite of lower nutrient supply from sediment, high EEA in surface water occurred later than the serious blooms, showing that the nutrient regeneration from sediment, not water body, was still the trigger for the start of the bloom, and sediment nutrient release and predominant surface water nutrient regeneration by abundant exoenzymes sustained the algal blooms. In the Western region, algal bloom started in the northern area and further spread in the remaining part of the lake; nutrient regeneration in the surface water sustained the slight bloom. In the East Bays, the decay and decomposition of macrophytes led to anaerobic conditions in sediments and high ammonia in interstitial water, but low iron bound phosphorus resulted in anaerobic release of very few P, thus showed extremely low Chl. a concentration.

Biogeochemical cycling of trace elements and nutrients in ferruginous waters: Constraints from a deep oligotrophic ancient lake

AbstractIron‐rich, ferruginous waters were the dominant geochemical regime for most of Earth's history. Modern ferruginous waters are found in stratified, sulfur‐poor lakes, and serve as crucial analogs for biogeochemical cycling throughout Earth's past. Here we present the first depth‐resolved data of physical structure, nutrients and trace elements from Lake Poso (Indonesia), a deep oligotrophic ancient lake. Lake Poso is ferruginous, with anoxia below ~ 90 m depth, placing it among the world's largest ferruginous lakes. Physical stratification is weaker than other tropical anoxic lakes, indicating sensitivity for paleoclimate reconstructions. Trace elements and nutrients are predominantly shaped by the oxic–anoxic transition. Manganese– and Fe oxyhydroxide–driven biogeochemical cycling occurs at distinct depth horizons, with Co and Ni controlled by Mn and showing shallow release in anoxic waters, while V, Cr, P, and As are controlled by Fe, with release in surface sediments and diffusive transport. Chromium is nonquantitatively removed in anoxic waters, in contrast to widespread assumptions in Cr‐based paleoreconstructions. Oxycline U and Se removal corresponds to a local N minimum, suggesting biological reduction and/or uptake. These first ferruginous water Se data also show removal in sediments, indicating sediment signals reflect multiple removal processes and informing Se‐based paleoreconstructions, while the absence of sediment U removal contrasts other anoxic basins. A comparison with other ferruginous lakes demonstrates how local influences drive deviations from expectations in other systems, and highlight common, generalizable ferruginous basin features. Therefore, these data will guide research in ferruginous settings across space and time, and improve paleoreconstructions from ferruginous sediment records.

Removal of enrofloxacin as well as nutrients in mariculture water by Sesuvium portulacastrum system: Insights for biodegradation, ecotoxicity of enrofloxacin

Antibiotic contamination and eutrophication in mariculture have become problems that cannot be ignored, and enrofloxacin (ENR), as an example, is especially widely used in mariculture. This study firstly revealed that Sesuvium portulacastrum, a plant with world-wide distribution in coastal zones, with its rhizosphere microorganisms, could remove ENR as well as nutrients. The S. portulacastrum system could degrade ENR to small-molecule products 1,2,3,4-tetrahydroquinolin-4-ol and (2,4-dihydroxyphenyl)-cyclopropylamine. And there were 81.3–39.2 % removals of ENR with 0.01-100 mg/L. Although ENR significantly influenced functions of rhizosphere microbial community, like decreasing nitrogen fixation, shifting trophic strategies from phototrophy to chemoheterotrophy, nutrients (NH4+-N, NO2−-N, NO3−-N and total dissolved phosphorus) removal of S. portulacastrum system was essentially unaffected at low ENR concentration (< 1 mg/L). The removal mechanism of S. portulacastrum system was explored. Neither of the isolated root exudates and rhizosphere bacteria could degrade ENR, however, without rhizosphere bacteria, ENR removal rate would decrease. Root proteins including oxidase, decarboxylase, dehydrogenase, such as laccase, isocitrate dehydrogenase, delta-1-pyrroline-5-carboxylate dehydrogenase were overexpressed. Additionally, endocytosis is a pathway for antibiotics to enter S. portulacastrum. This study demonstrated that S. portulacastrum system could be used for remediation of antibiotics-nutrients combined pollution, and deepened understanding the antibiotic removal mechanism of macrophytes in mariculture, moreover, provided new macroplant species and a theoretical basis for antibiotics removal in aquatic systems.

Trace element distribution, sources, toxicity risk characteristics associated with lacustrine groundwater discharge in boreal lakes: Implications for the eco-environmental security in the Yellow River Basin, China

Although the pollution of trace elements has been extensively studied, there is still a lack of comprehensive understanding regarding accumulation of these elements in lake ecosystems within the Yellow River basin, specifically the effects of lacustrine groundwater discharge (LGD) on trace elements. This study investigated the distribution, sources, and toxicity risks associated with 20 target trace elements (i.e., Li, Sc, Ti, V, Mn, Cr, Co, Ni, Cu, Zn, Rb, Y, Mo, Sb, Ba, W, Tl, Pb, U and Sr) in lake water (LW), groundwater (GW), and river water (RW) influenced by the LGD process in lake Ulansuhai and lake Daihai. The natural source is the primary contributor of trace elements in both LW and GW within the two lake basins, while industrial discharge plays a secondary role. The average LGD fluxes in lake Ulansuhai and Daihai basins were 6.39 × 105 m3/d and 1.07 × 105 m3/d, respectively. Additionally, the trace element fluxes from LGD in lake Ulansuhai (mean of 106,659.37 g/d) exceeded those observed in lake Daihai (mean of 3236.57 g/d). The overall toxicity risk was found to be higher in lake Ulansuhai (LW (17.36) > RW (16.81) > GW (12.76)) compared to lake Daihai (GW (10.43) > LW (9.10) > RW (4.63)). As well as the toxicity levels of trace elements in lake Ulansuhai were elevated compared to Daihai, which can be attributed to the influenced of ion compositions and water nutrients. Among them, Ca2+, Mg2+, and SO42+ were identified as key ions impacting the toxicity of trace elements in lake Ulansuhai. These findings provide crucial insights for targeted monitoring and mitigation of trace element pollution in the Yellow River basin’s lake ecosystems.

The effects of long-term radiation exposure on the reproductive structures of Glyceria maxima (Hartm.) Holmb.: A case study in the Chornobyl exclusion zone

During the acute phase of the Chornobyl accident the biota of the contaminated area was exposed to high doses of ionising radiation. Although these doses decreased significantly over the years, the exposure persisted over a prolonged period. This long-term exposure can be considered as a direct cause of genetic modifications occurring in organisms, and the search for correlative changes in the state of biota under the impact of radioactive contamination is an extremely urgent task. The aquatic macrophyte Glyceria maxima is the most common coenosis-forming plant of the littoral vegetation of the floodplain water bodies in the Chornobyl Exclusion Zone, and is capable of concentrating radionuclides in significant quantities. In this study, we aim to determine whether long-term radiation exposure has affected organs of reproductive structure (flower, pollen, seed) and, consequently, the viability of local populations of this species. All the traits analysed showed an inverse relationship with the absorbed dose rate of the maternal plants. It was determined that with an increase in the absorbed dose rate, the pollen size decreases, and the range of individual grains in the sample begins to vary more: small, heterogeneous in shape and size pollen grains are formed. Additionally, a decrease in pollen grain size correlates with a decrease in the proportion of fertile pollen. Pollen grains viability (fertility) decreases by 20–40% with increasing radiation dose rate. The response of reproductive structures to radiation exposure is non-linear: already at low doses (>2 μGy/h), negative changes in functional and morphological traits are observed, while at higher doses (9–13 μGy/h), the changes slow down. It is assumed that the radiation exposure mainly affects the early reproductive stages (pollen grains and partially flowers), while the main nutrients in water, that determine the trophic status of the reservoir, affects the late stages (seeds).

Study of nitrogen and phosphorus nutrient dynamics in concentrated marine fish farming water environment in Long Son - Vung Tau

The nutritional content of N and P in concentrated marine fish farming water in the Cha Va - Long Son - Vung Tau estuary area increased sharply during 2013–2016; notably, the N-NH4+ content increased in 2017–2019. The N-NO2- and N-NO3- content in the dry season (0.051 mg/L and 0.190 mg/L) was higher than in the rainy season (0.044 mg/L and 0.133 mg/L). In contrast, the N-NH4+ and P-PO43- contents in the rainy season (0.321 mg/L and 0.1 mg/L) are higher than in the dry season (0.154 mg/L and 0.093 mg/L). The N and P nutrient dynamics in water fluctuate according to the semi-diurnal tide regime; the nutrient content decreases during high water - daytime, increases during low water in the evening, and is high during high water at night and in the morning, early the next day. In dry and rainy seasons, the N-NH4+ content is always the highest (0.024–0.761 mg/L) among the nitrogen-based nutritional parameters. N and P nutrients in water are correlated: N-NH4+ parameter pairs with Total P, N-NO2- with Total P, Total N with Total P, N-NO2- and N-NO3-, P-PO43- with Total P, and the parameter pair N-NO2- with P-PO43- have low positive correlation coefficients (r), from 0.1–0.21. Conversely, the parameter pairs N-NO3- and Total N, N-NO3- and N-NH4+, and N-NO2- and N-NH4+ have low negative correlation coefficients (r), from -0.12 to -0.26. From 2010–2021, the number of cages increased beyond planning, causing environmental pollution in the water in the farming area. The nutritional RQ value of the water is high at level 4 every year (very high risk of environmental pollution).

Improving the identification of pollution source areas with catchment-resolution sensitivity analysis

The significant impacts of total nitrogen (TN) and total phosphorus (TP) on riverine ecosystems underscores the critical need to identify the primary nutrient source areas in watersheds. This study aims to unravel the influences of terrain and land use types on mean monthly TN (TNM) and mean monthly TP (TPM) export across varying catchment resolutions in the Qiantang River Watershed of China. The findings of this study illuminated the critical role of topography in understanding nutrient dynamics, wielding a profound influence over water flow patterns and nutrient dispersion. Both land slope and Stream Power Index (SPI) displayed substantial negative correlations (r < −0.6) with TNM and TPM concentrations, whereas the Topographic Wetness Index (TWI) showed positive correlations with the nutrient indexes. In addition to terrain characteristics, impervious land surfaces had a positive correlation with nutrient concentrations, while grassland and forest areas exhibited negative correlations. Results further underscored the substantial influence of catchment resolution on correlations between watershed properties and riverine nutrient concentrations. It was imperative to choose an effective catchment resolution in watershed delineation – not too coarse, nor too fine – to accurately capture the topographic and land use impacts on nutrient dynamics. With the most appropriate catchment size (Catchment 700 km2), the critical pollution source areas for TN and TP pollution were identified, and thus could be used to guide future pollution reduction efforts. The study not only highlights the importance of identifying an appropriate catchment size for water pollution, but also emphasizes the necessity of effectively extracting critical pollution source areas to mitigate water nutrient pollution and increase the ecological integrity of the Qiantang River Watershed.

Combining effects of submerged macrophytes and lanthanum-modified bentonite on sediment enzyme activity: Evidence from mesocosm study

Lanthanum-modified bentonite (LMB) combined with submerged macrophytes (SM) has been a conventional means of eutrophication management in lakes in recent years, and is one of the most important methods for P removal. However, trends in nutrients and sediment enzymes at the water-sediment interface during this process have not been systematically assessed, and there are still some gaps in how abiotic properties drive changes in enzyme activity. Here, we show changes in aquatic environmental conditions under the action of different ratios of modified bentonite (0, 10%, 20%, and 30%) in combination with SM (Vallisneria natans, Potamogeton lucens, and Hydrilla verticillate) and quantify their effects on sediment enzyme activities. The results showed that the nutrient cycling at the water-sediment interface was facilitated by the combined effect of SM and LMB, which effectively reduced the overlying water nutrient concentration, increased the sediment enzyme activity and enhanced the N cycling process. Partial least squares structural equation model (PLS-SEM) showed that sediment parameters strongly influenced changes in enzyme activity, with NO3–N as the main controlling factors. Our study fills in the process of changing environmental conditions in lake water under geoengineered materials combined with macrophyte measures, especially the changes in biological properties enzyme activities, which contributes to a clearer understanding of nutrient fluxes during the management of eutrophication in lakes.

Virus communities rather than bacterial communities contribute more on nutrient pool in polluted aquatic environment

The degradation of animal carcasses can lead to rapid waste release (e.g., pathogenic bacteria, viruses, prions, or parasites) and also result in nutrient accumulation in the surrounding environment. However, how viral profile responds and influences nutrient pool (carbon (C), nitrogen (N), phosphorus (P) and sulfur (S)) in polluted water caused by animal carcass decomposition had not been explored. Here, we combined metagenomic analysis, 16S rRNA gene sequencing and water physicochemical assessment to explore the response of viral communities under different temperatures (23 °C, 26 °C, 29 °C, 32 °C, and 35 °C) in water polluted by cadaver, as well as compare the contribution of viral/bacterial communities on water nutrient pool. We found that a total of 15,240 viral species were classified and mainly consisted of Siphoviridae. Both temperature and carrion reduced the viral diversity and abundance. Only a small portion of the viruses (∼8.8 %) had significant negative correlations with temperature, while most were not sensitive. Our results revealed that the viruses had lager contribution on nutrient pool than bacteria. Besides, viral-related functional genes involved in C, N, P and S cycling. These functional genes declined during carcass decomposition and covered part of the central nutrient cycle metabolism (including carbon sugar transformation, denitrification, P mineralization and extracelluar sulfate transfer, etc.). Our result implies that human regulation of virus communities may be more important than bacterial communities in regulating and managing polluted water quality and nutrition

Effects of water nutrient concentrations on stream macroinvertebrate community stoichiometry: a large-scale study

Effects of water nutrient concentrations on stream macroinvertebrate community stoichiometry: a large-scale study

Chromophoric dissolved organic matter traces seasonally changing coastal processes in a river-influenced region of the western Bay of Bengal.

The optical characteristics of colored dissolved organic matter (CDOM) serve as a convenient tool for evaluating coastal processes, e.g., river runoff, anthropogenic inputs, primary production, and bacterial/photochemical processes. We conducted a study on the seasonal and spatial variability of absorbance and fluorescence characteristics of CDOM and nutrients in the coastal waters near the Gauthami estuary of River Godavari, the largest peninsular river of India, for a year. The surface aCDOM(350) showed a significant inverse relation with salinity in the coastal region, indicating a conservative mixing of marine and terrestrial end members. The aCDOM(350) was not conservative in the offshore (100m isobath) waters due to enrichment by secondary sources. Seasonal variability in optical properties indicated diverse sources for CDOM, as revealed by principal component analysis. The excitation-emission matrix (EEM) spectra followed by parallel factor analysis (EEM-PARAFAC) revealed four distinct fluorophores. The tyrosine (B) fluorophore showed a predominant increase in the post-monsoon season (October to January), while tryptophan (T) was relatively more enriched, coincident with nutrient enrichment and transparency increase during the early monsoon phase (July). The biological index (BIX), which reflects recent photosynthetic activity, also displayed relatively higher values during the early monsoon. The humic fluorophores A and M, and humification index (HIX) were relatively enriched during the later phase of monsoon (July-October). HIX was > 4 in a few samples of the offshore region (100-m isobath) and indicated a probable contamination from drill-mud (bentonite) used in hydrocarbon exploration. During the monsoon, the relationship between T and B with CDOM was not evident due to the masking of B fluorescence in intact protein. However, during the post-monsoon (POM) and pre-monsoon (PRM) periods, this masking effect was not observed, likely due to protein degradation via bacterial and photochemical processes, respectively. Temporal variability in nutrients indicated that high ammonium levels were produced during POM (OM bacterial degradation), and high nitrite levels were observed during PRM (due to primary production). This study provides foundational insights into the use of CDOM for understanding the impact of diverse environmental, river discharge, and anthropogenic factors on coastal ecosystems.

Planktonic foraminifera response to the azores high and industrial-era global warming in the central-western Mediterranean Sea

The Mediterranean Sea is warming about 20 % more rapidly than global ocean and this phenomenon is impacting ecosystems and biodiversity. Planktonic foraminifera are an important component of surface and subsurface water ecosystems and food chains. Their species communities have been altering across the oceans since the Industrial Era, in response to the ongoing climate change, especially in the western Mediterranean Sea, where a significant productivity decrease has been recently reported.Here we show planktonic foraminifera and multispecies stable isotopes from three short sediment cores, recovered on the eastern flank of the Sicily Channel, central Mediterranean Sea. Results fully confirm the planktonic foraminifera productivity decrease in the Industrial Era, which is especially relevant for the second half of the 20th century. The planktonic foraminifera productivity decrease matches with a higher number of Large Azores High events, i.e., the establishment of an exceptional and persistent winter atmospheric high-pressure ridge over the western-central Mediterranean Sea. This is an unprecedented atmospheric phenomenon for the last millennia Mediterranean Sea history, as a direct response of the global warming. Surface productivity and DCM species are especially declining since ∼1960 CE, at expenses of winter mixed layer taxa, suggesting that the Azores High activity prevents a sustained water column vertical mixing and surface water nutrient fuelling. Our results document and confirm that the climate change has already been affecting Mediterranean marine ecosystems and the basic level of the trophic chain, by extending the surface water stratification period.

Lake Water Ecological Simulation for a Typical Alpine Lake on the Tibetan Plateau

Lakes on the Tibetan Plateau (TP) serve as both indicators of and safeguards against climate change, playing a crucial role in the aquatic ecosystems of the TP. While considerable attention has been devoted to studying the thermal and dynamic processes of TP lakes, research focusing on their ecological variations has been limited. In this study, we selected Namco, a representative lake on the TP, to investigate its water ecological processes using the AQUATOX lake ecological model. Long-term ecological variations spanning from 1980 to 2020 were analyzed based on lake observations. Our results revealed a consistent increase in water nutrients, particularly total nitrogen (WTN), and total phosphorus (WTP), over the study period. Additionally, the concentrations of chlorophyll-a (Chl-a) and water gross and net primary production (WGPP and WNPP) exhibited a significant upward trend. Despite the persistent state of poor nutrition in the lake, the ecological conditions improved. Multiple linear regression analysis indicated that the concentrations of WGPP, WNPP, and Chl-a were more sensitive to the local climate and hydrology compared to WTN and WTP. A continuously warming climate would heat up the lake water body, further enhancing primary production and improving water quality in the future. This study provides insights for lake limnological and ecological research and can be used to inform water management strategies in high-altitude alpine regions.

Nutrient leaching potential along a time series of forest water reclamation facilities in northern Idaho

Forest water reclamation is a decades-old practice of repurposing municipal reclaimed water using land application on forests to filter nutrients and increase wood production. However, long-term application may lead to nutrient saturation, leaching, and potential impairment of ground and surface water quality. We studied long-term effects of reclaimed water application on nutrient leaching potential in a four-decade time series of forest water reclamation facilities in northern Idaho. Our approach compared reclaimed water treated plots with untreated control plots at each of the forest water reclamation facilities. We measured soil nitrifier abundance and net nitrification rates and used tension lysimeters to sample soil matrix water and drain gauges to sample from a combination of matrix and preferential flow paths. We determined nutrient leaching as the product of soil water nutrient concentrations and model-estimated drainage flux. There was more than 450-fold increase in nitrifier abundance and a 1000-fold increase in net nitrification rates in treated plots compared with control plots at long-established facilities, indicating greater nitrate production with increased cumulative inputs. There were no differences in soil water ammonium, phosphate, and dissolved organic nitrogen concentrations between control and effluent treatments in tension lysimeter samples. However, concurrent with increased nitrifier abundance and net nitrification, nitrate concentration below the rooting zone was 2 to 4-fold higher and nitrate leaching was 4 to 10-fold higher in effluent treated plots, particularly at facilities that have been in operation for over two decades. Thus, net nitrification and nitrifier abundance assays are likely indicators of nitrate leaching potential. Inorganic nutrient concentrations in drain gauge samples were 2 to 11-fold higher than lysimeter samples, suggesting nutrient losses occurred predominantly through preferential flow paths. Nitrate was vulnerable to leaching during the wet season under saturated flow conditions. Although nitrogen saturation is a concern that should be mitigated at long-established facilities, these forest water reclamation facilities were able to maintain average soil water nitrate concentrations to less than 2 mg L−1, so that nitrogen and phosphorous are effectively filtered to below safe water standards.

Dams alter the control pattern of watershed land use to riverine nutrient distribution: Comparison of three major rivers under different hydropower development levels in Southwestern China

Land use plays a critical role in managing water quality in a watershed, as it governs the import and distribution of nutrients. In addition to the land use, some rivers in Southwest China are encountering a new environmental stressor of damming, which is being driven by the national strategy of hydropower development. However, the coupling effect of land use and dams on nutrients remains poorly understood, challenging the effective management of riverine water quality. Therefore, this study examined the nutrients in the Nu, Yarlung Tsangpo (YT), and Lancang (LC) Rivers, which have no dam, 1 dam, and 11 dams, respectively, during different regulatory periods (spring and fall) to identify variations in nutrient control patterns influenced by land use and dams. The findings suggested that an increase in hydropower development contributed to a notable shift in nutrient patterns from land use regulation towards dam regulation and coupling effects. Land use dominated the nutrient variations of the Nu (27.4 %–32.8 %) and low hydropower development YT (25.2 %–30.9 %) Rivers during both seasons, but the primary contributors to the nutrient variations of the high hydropower development LC River were dams (17.9 %–41.6 %) and coupling effects (16.5 %–29.0 %). Dams transform nutrient levels and compositions through internal reservoir cycling, decoupling land use and nutrients. Partial least-squares structural equation model analysis further suggested that the coupling effects of the LC River were seasonal-specific, which was primarily attributed to hydrological variations that affected their interactions. During spring, the reservoir underwent a drainage mode characterized by high-level nutrients in the bottom water. Combined with the import of riverine nutrients, it exacerbated the increase of nutrients (synergistic effect). In contrast, the reservoir transitioned into a storage mode where it intercepted nutrients from the upstream and watershed during the fall, leading to a reduction in the previously observed increasing trend and an increase in nutrient variability (antagonism effect).

Metropolitan pressures: Significant biodiversity declines and strong filtering of functional traits in fish assemblages

Accelerating global urbanization is leading to drastic losses and restructuring of biodiversity. Although it is crucial to understand urban impacts on biodiversity to develop mitigation strategies, there is a dearth of knowledge on the functional structure of fish assemblages spanning the entire city-scale spectrum of urbanization intensity. Here, using environmental DNA sampled from 109 water sites in Beijing, we investigated the taxonomic and functional diversity patterns of fish assemblages across the city and uncovered community-, trait-, and species-level responses to various environmental stressors. By ranking sampling sites into three disturbance levels according to water physiochemical and landcover conditions, we found that both native and non-native fish taxonomic and functional α-diversity decreased significantly with elevating disturbance, as strong disturbance led to the disappearance of many species. However, the quantitative taxonomic and functional β-diversity components of native and non-native fish showed distinct patterns; assemblage turnover dominated native fish β-diversity and decreased with increasing disturbance, whereas species/trait richness differences dominated non-native fish β-diversity and increased with disturbance intensity particularly in lotic waters. RLQ and fourth-corner analyses revealed that fish size, fecundity, diet, and reproductive behaviors were significantly correlated with water quality, with pollution-tolerant, larger-sized native and omnivorous non-native fishes being urban winners, which indicates strong trait-dependent environmental filtering. Potential ecological indicator species were identified based on the sensitivity of fish responses to pollution loads; these were mostly small native species, and many have bivalve-dependent reproduction. Our results demonstrate that, along with native fish assemblage simplification and homogenization, urban stressors exert profound impacts on community trait composition, highlighting the need to consider both biodiversity loss and functional reorganization in combating disturbance of aquatic ecosystems under global urbanization. Furthermore, correlations between cropland cover and water nutrient level suggested that the management of agricultural runoff might be critically important for safeguarding urban water quality.