SciCombinator

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Concept: Eutrophication

170

Macrophyte decomposition is important for carbon and nutrient cycling in lake ecosystems. Currently, little is known about how this process responds to detritus quality and water nutrient conditions in eutrophic shallow lakes in which incomplete decomposition of detritus accelerates the lake terrestrialization process. In this study, we investigated the effects of detritus quality and water nutrient concentrations on macrophyte decomposition in Lake Baiyangdian, China, by analyzing the decomposition of three major aquatic plants at three sites with different pollution intensities (low, medium, and high pollution sites). Detritus quality refers to detritus nutrient contents as well as C:N, C:P, and N:P mass ratios in this study. Effects of detritus mixtures were tested by combining pairs of representative macrophytes at ratios of 75:25, 50:50 and 25:75 (mass basis). The results indicate that the influence of species types on decomposition was stronger than that of site conditions. Correlation analysis showed that mass losses at the end of the experimental period were significantly controlled by initial detritus chemistry, especially by the initial phosphorus (P) content, carbon to nitrogen (C:N), and carbon to phosphorus (C:P) mass ratios in the detritus. The decomposition processes were also influenced by water chemistry. The NO(3)-N and NH(4)-N concentrations in the lake water retarded detritus mass loss at the low and high pollution sites, respectively. Net P mineralization in detritus was observed at all sites and detritus P release at the high pollution site was slower than at the other two sites. Nonadditive effects of mixtures tended to be species specific due to the different nutrient contents in each species. Results suggest that the nonadditive effects varied significantly among different sites, indicating that interactions between the detritus quality in species mixtures and site water chemistry may be another driver controlling decomposition in eutrophic shallow lakes.

Concepts: Oxygen, Plant, Lake, Eutrophication, Hydrogen, Water pollution, Nitrogen, Lakes

95

In 2011, Lake Erie experienced the largest harmful algal bloom in its recorded history, with a peak intensity over three times greater than any previously observed bloom. Here we show that long-term trends in agricultural practices are consistent with increasing phosphorus loading to the western basin of the lake, and that these trends, coupled with meteorological conditions in spring 2011, produced record-breaking nutrient loads. An extended period of weak lake circulation then led to abnormally long residence times that incubated the bloom, and warm and quiescent conditions after bloom onset allowed algae to remain near the top of the water column and prevented flushing of nutrients from the system. We further find that all of these factors are consistent with expected future conditions. If a scientifically guided management plan to mitigate these impacts is not implemented, we can therefore expect this bloom to be a harbinger of future blooms in Lake Erie.

Concepts: Algae, Cyanobacteria, Time, Water, Eutrophication, Algal bloom, Phosphorus, Dinoflagellate

86

Urban water systems are impacted by land use within their source watersheds, as it affects raw water quality and thus the costs of water treatment. However, global estimates of the effect of land cover change on urban water-treatment costs have been hampered by a lack of global information on urban source watersheds. Here, we use a unique map of the urban source watersheds for 309 large cities (population > 750,000), combined with long-term data on anthropogenic land-use change in their source watersheds and data on water-treatment costs. We show that anthropogenic activity is highly correlated with sediment and nutrient pollution levels, which is in turn highly correlated with treatment costs. Over our study period (1900-2005), median population density has increased by a factor of 5.4 in urban source watersheds, whereas ranching and cropland use have increased by a factor of 3.4 and 2.0, respectively. Nearly all (90%) of urban source watersheds have had some level of watershed degradation, with the average pollutant yield of urban source watersheds increasing by 40% for sediment, 47% for phosphorus, and 119% for nitrogen. We estimate the degradation of watersheds over our study period has impacted treatment costs for 29% of cities globally, with operation and maintenance costs for impacted cities increasing on average by 53 ± 5% and replacement capital costs increasing by 44 ± 14%. We discuss why this widespread degradation might be occurring, and strategies cities have used to slow natural land cover loss.

Concepts: Water, Eutrophication, Water pollution, City, Pollution, Land use, Rural economics, Land cover

54

Phosphorus losses from land to water will be impacted by climate change and land management for food production, with detrimental impacts on aquatic ecosystems. Here we use a unique combination of methods to evaluate the impact of projected climate change on future phosphorus transfers, and to assess what scale of agricultural change would be needed to mitigate these transfers. We combine novel high-frequency phosphorus flux data from three representative catchments across the UK, a new high-spatial resolution climate model, uncertainty estimates from an ensemble of future climate simulations, two phosphorus transfer models of contrasting complexity and a simplified representation of the potential intensification of agriculture based on expert elicitation from land managers. We show that the effect of climate change on average winter phosphorus loads (predicted increase up to 30% by 2050s) will be limited only by large-scale agricultural changes (e.g., 20-80% reduction in phosphorus inputs).The impact of climate change on phosphorus (P) loss from land to water is unclear. Here, the authors use P flux data, climate simulations and P transfer models to show that only large scale agricultural change will limit the effect of climate change on average winter P loads in three catchments across the UK.

Concepts: Agriculture, Eutrophication, Climate, Ecosystem, United Kingdom, Management, Climate change, Aquatic ecosystem

50

Increasing diffuse nitrate loading of surface waters and groundwater has emerged as a major problem in many agricultural areas of the world, resulting in contamination of drinking water resources in aquifers as well as eutrophication of freshwaters and coastal marine ecosystems. Although empirical correlations between application rates of N fertilizers to agricultural soils and nitrate contamination of adjacent hydrological systems have been demonstrated, the transit times of fertilizer N in the pedosphere-hydrosphere system are poorly understood. We investigated the fate of isotopically labeled nitrogen fertilizers in a three-decade-long in situ tracer experiment that quantified not only fertilizer N uptake by plants and retention in soils, but also determined to which extent and over which time periods fertilizer N stored in soil organic matter is rereleased for either uptake in crops or export into the hydrosphere. We found that 61-65% of the applied fertilizers N were taken up by plants, whereas 12-15% of the labeled fertilizer N were still residing in the soil organic matter more than a quarter century after tracer application. Between 8-12% of the applied fertilizer had leaked toward the hydrosphere during the 30-y observation period. We predict that additional exports of (15)N-labeled nitrate from the tracer application in 1982 toward the hydrosphere will continue for at least another five decades. Therefore, attempts to reduce agricultural nitrate contamination of aquatic systems must consider the long-term legacy of past applications of synthetic fertilizers in agricultural systems and the nitrogen retention capacity of agricultural soils.

Concepts: Agriculture, Water, Fertilizer, Eutrophication, Soil, Nitrogen, Phosphorus, Manure

28

Inorganic nitrate has been shown to reduce oxygen cost during exercise. Since the nitrate-nitrite-NO pathway is facilitated during hypoxia, we investigated the effects of dietary nitrate on oxygen consumption and cardiovascular responses during apnea. These variables were measured in two randomized, double-blind, placebo-controlled, crossover protocols at rest and ergometer exercise in competitive breath-hold divers. Subjects held their breath for predetermined times along with maximum effort apneas after two separate 3-day periods with supplementation of potassium nitrate/placebo. In contrast to our hypothesis, nitrate supplementation led to lower arterial oxygen saturation (SaO(2), 77±3%) compared to placebo (80±2%) during static apnea, along with lower end-tidal fraction of oxygen (FETO(2)) after 4min of apnea (nitrate 6.9±0.4% vs. placebo 7.6±0.4%). Maximum apnea duration was shorter after nitrate (329±13s) compared to placebo (344±13s). During cycle ergometry nitrate had no effect on SaO(2), FETO(2) or maximum apnea duration. The negative effects of inorganic nitrate during static apnea may be explained by an attenuated diving response.

Concepts: Oxygen, Carbon dioxide, Blood, Effect, Eutrophication, Free-diving

28

Leaking sewer infrastructure contributes non-point nitrogen pollution to ground- and surface water in urban watersheds. However, these inputs are poorly quantified in watershed budgets, potentially underestimating pollution loadings. In this study, we used inverse methods to constrain dissolved inorganic nitrogen (DIN) inputs from sewage to Nine Mile Run (NMR), an urban watershed in Pittsburgh, Pennsylvania (USA). NMR drains a 1,570 ha watershed characterized by extensive impervious surface cover (38%) and surface and groundwater impacts from combined sewer overflows and leaky sewers. Water samples were collected bi-weekly over two years and intensive sampling was conducted during one summer storm. A nitrogen budget for the NMR watershed was built using known inputs/exports and retention estimates from published studies. These variables were ultimately inverted and sewage DIN inputs constrained using Monte Carlo simulation. Results indicate that DIN contributions from sewage range from 6 to 14 kg ha-1yr-1. When reasonable estimates of inputs are considered, the NMR budget cannot be balanced without taking sewage into account. Further, when conservative estimates of DIN from sewage are included in input calculations, DIN retention in NMR is comparable to high rates observed in other suburban/urban nutrient budgets (maximum likelihood retention estimate=84%).

Concepts: Agriculture, Water, Eutrophication, Water pollution, Hydrology, Monte Carlo, Sanitary sewer, Strategic misrepresentation

26

A comprehensive monitoring program was conducted to investigate the nutrient spatial pattern in the mainstream of the Yangtze River from the Baihetan Dam down to the Three Gorges Dam located at the upper region of the Yangtze River in China. Samples were taken from 33 different sites from July 30 to August 19, 2011. The nutrient patterns of the three representative tributaries of the Three Gorges Reservoir (TGR)-the Modao, the Daning, and the Xiangxi Rivers-were also investigated. The results show that the mainstream of the TGR has a higher concentration of nitrogen and a lower concentration of phosphorus than that of the upper mainstream before the TGR. Moreover, it was found that nitrate-nitrogen (NO3-N) is the main nitrogen component, while particulate phosphorus predominates the total phosphorus (TP). It was found that the three representative tributaries of the TGR have lower total nitrogen (TN) concentrations compared to the corresponding sections of the mainstream TGR. Based on the nutrient spatial pattern, the nutrient flux was calculated. The total fluxes of TN, NO3-N, TP, and orthophosphate (PO4-P) from the upstream reach into the TGR are 2,155.06, 1,674.97, 212.98, and 83.42 t day(-1), respectively. The amount of nutrients imported from the TGR into its tributaries is more than the amount exported. It was determined that the Xiangxi River has the largest net rate of imported nitrogen at 7.66 t day(-1), whereas the Daning River has the largest net rate of imported phosphorus at 1.75 t day(-1). In addition, compared with the nutrients imported from the TGR into its tributaries, the nutrient flux from the upstream reach into the TGR contributes approximately less than 3 %.

Concepts: Eutrophication, Yangtze River, Chongqing, Dam, Three Gorges Dam, Hubei, Three Gorges, Yichang

25

Macrophyte combined with artificial aeration is a promising in situ remediation approach for urban rivers polluted with nutrients and organic matter. However, seasonal variations and aeration effects on phytoremediation performance and root-adhered microbial communities are still unclear. In this study, Pontederia cordata was used to treat polluted urban river water under various aeration intensities. Results showed that the highest removal efficiencies of chemical oxygen demand (CODCr) and total nitrogen (TN) were attained under aeration of 30 L min(-1) in spring and summer and 15 L min(-1) in autumn, while total phosphorus (TP) removal reached maximum with aeration of 15 L min(-1) in all seasons. Moderate aeration was beneficial for increasing the diversity of root-adhered bacteria communities, and the shift of bacterial community structure was more pronounced in spring and autumn with varying aeration intensity. The dual effect, i.e. turbulence and dissolved oxygen (DO), of aeration on the removal of CODCr and TN prevailed over the individual effect of DO, while DO was the most influential factor for TP removal and the root-adhered bacterial community diversity. P. cordata combined with 15 L min(-1) aeration was deemed to be the best condition tested in this trial study.

Concepts: Oxygen, Bacteria, Water, Eutrophication, Soil, Nitrogen, Season, Microorganism

23

Ecological criteria are needed for a comprehensive evaluation of groundwater ecosystem health by including biological components with the physical and chemical properties that are already required by European directives. Two methodological approaches to assess the ecological status of groundwater ecosystems were combined in two alluvial plains (the Ariège and Hers Rivers, southwestern France) varying in agriculture intensity (from grassland to crop rotation including maize and sunflower, and to maize monoculture). In the first approach, the composition of invertebrate assemblages (only obligate-groundwater crustaceans, i.e. stygobionts) sampled in 28 wells differing in their land use contexts was analysed. Abundance, species richness, and assemblage composition significantly changed with agricultural land use or urbanization around the wells. In the second approach, we tested an in situ exposure of sentinel organisms to quantify their response to the environmental pressures. The epigean and native amphipod species Gammarus cf. orinos was used as the sentinel species. Amphipods (30 individuals in each of 10 wells) were exposed for one week to the in situ conditions at two seasons with contrasted concentrations of pollutants. The Ecophysiological Index (EPI) synthetizing the survival rates and energetic storage decreased in wells with low oxygen and high nitrate concentrations, but only during the highest contamination period. Atrazine-related compounds negatively impacted sentinel health whatever the season. The combination of these two approaches may have major applications for orientating groundwater ecosystem management.

Concepts: Biodiversity, Agriculture, Biology, Organism, Life, Ecology, Eutrophication, Crustacean