Nutrient Mitigation Research Articles

Nitrogen and Phosphorous Content in Blue Mussels (Mytilus spp.) Across the Baltic Sea

To support the ongoing discussion about mussel farming and the potential to extract nutrients from the sea, this study investigated the phosphorus (P) and nitrogen (N) content of blue mussels (Mytilus spp.) under different abiotic and biotic parameters. The focus of this survey was on the highly eutrophied Baltic Sea, where salinity ranges from 4 to 27 psu, and is a major contributing factor to differential mussel growth. We observed that nutrient content was not linearly correlated to salinity, but if categorized, decreased at higher salinities. Chlorophyll-a and temperature did not significantly correlate with nutrient content, but season of harvest and mussel size did. Furthermore, habitat was a strong driver of nutrient content, indicating higher nutrient density if mussels are grown in mussel farms (i.e. in the water column) instead of on mussel culture beds or harvested from wild beds (on the sea bed). Values of N and P averaged 5.85 % N and 0.83 % P of tissue dry weight in mussels at the sea bed and 9.43 % N and 0.96 % P of tissue dry weight in mussels from longline cultivation. These results will be useful in refining estimations about mussel farming as a nutrient mitigation measure and the extraction potential, as well as related costs.

Nitrogen soil surface budgets for districts in Germany 1995 to 2017

BackgroundNitrogen (N) as a key input for crop production has adverse effects on the environment through emissions of reactive nitrogen. Less than 20% of the fertiliser nitrogen applied to agricultural land is actually consumed by humans in meat. Given this situation, nitrogen budgets have been introduced to quantify potential losses into the environment, to raise awareness in nutrient management, and to enforce and monitor nutrient mitigation measures. The surplus of the N soil surface budget has been used for many years for the assessment of potentially water pollution with nitrate from agriculture.ResultsFor the 402 districts in Germany, nitrogen soil surface budgets were calculated for the time series 1995 to 2017. For the first time, biogas production in agriculture and the transfer of manure between districts were included in the budget. Averaged for all districts, the recent N supply to the utilised agricultural area (UAA) totals 227 kg N ha−1 UAA (mean 2015–2017), among them 104 kg N ha−1 UAA mineral fertiliser, 59 kg N ha−1 UAA manure, 33 kg N ha−1 UAA digestate, 14 kg N ha−1 UAA from gross atmospheric deposition, 13 kg N ha−1 UAA biological N fixation, and 1 kg N ha−1 UAA from seed and planting material. The withdrawal with harvested products accounts for 149 kg N ha−1 UAA, resulting in an N soil surface budget surplus of 77 kg N ha−1 UAA. The N surpluses per district (mean 2015–2017) vary considerably between 26 and 162 kg N ha−1 UAA and the nitrogen use efficiency of crop production ranges from 0.53 to 0.79 in the districts. The N surplus in Germany as a whole has remained nearly constant since 1995, but the regional distribution has changed significantly. The N surplus has decreased in the arable farming regions, but increased in the districts with high livestock density. Some of this surplus, however, is relocated to other districts through the transfer of manure.ConclusionsThe 23-year time series forms a reliable basis for further interpretation of N soil surface surplus in Germany. Agri-environmental programmes such as the limitation of the N surplus through the Fertiliser Ordinance and the promotion of biogas production have a clear effect on the N surplus in Germany as a whole and its regional distribution.

Multiple lines of evidence reveal complex rainbow trout responses to stream habitat enhancements

Abstract Habitat enhancements seek to ameliorate the detrimental effects of environmental degradation and take many forms, but usually entail structural (e.g. logs, cribs, reefs) or biogenic (e.g. carrion additions, vegetation plantings, fish stocking) augmentations with the intent of increasing fish annual production (i.e. accrual of new fish biomass through time). Whether efforts increase fish production or simply attract fish has long been subject to debate. Streams of the Pacific Northwest are commonly targeted for habitat enhancements to mitigate for the detrimental effects of dams and other forms of habitat degradation on Pacific salmon. Nutrient mitigation (i.e. the practice of artificially fertilising freshwaters) is a form of biogenic habitat enhancement that attempts to mimic the enrichment effects of a natural Pacific salmon spawning event. This approach assumes nutrient augmentations alleviate nutrient limitation of primary producers and/or food limitation of primary and secondary consumers, culminating in increased fish production. We conducted a multi‐year manipulative experiment and tracked responses of interior rainbow trout (Oncorhynchus mykiss) to annual additions of Pacific salmon carcasses as part of an effort to enhance the productivity of salmonid populations in streams where salmon runs have been lost. We employed an integrated approach to partition the mechanisms driving numerical responses of trout populations across timescales, to assess population turnover, and to track responses to habitat enhancements across individual to population level metrics. Short‐term numerical increases by trout were shaped by immigration and subsequently via retention of individuals within treatment reaches. As trout moved into treated stream reaches, individuals foraged, grew, and subsequently moved to other locations such that short‐term increases in fish numbers did not persist from year to year. All told, additions of salmon carcasses alleviated apparent food limitation and thereby increased secondary production of rainbow trout. However, at an annual time scale, increased production manifested as larger individual fish, not more fish within treated reaches. Fish movements and high population turnover within treated stream reaches apparently led to the subsequent dispersal of increased fish production. We found multiple lines of evidence that indicated that annual additions of salmon carcasses aggregated rainbow trout and enhanced their annual production. Through this replicated management experiment, we documented dynamic individual and population level responses to a form of stream habitat manipulation across weekly and annual timescales.

Nutrient mitigation under the impact of climate and land-use changes: A hydro-economic approach to participatory catchment management

Excessive nutrient loadings into rivers are a well-known ecological problem. Implemented mitigation measures should ideally be cost-effective, but perfectly ranking alternative nutrient mitigation measures according to cost-effectiveness is a difficult methodological challenge. Furthermore, a particularly practical challenge is that cost-effective measures are not necessarily favoured by local stakeholders, and this may impede their successful implementation in practice. The objective of this study was to evaluate the cost-effectiveness of mitigation measures using a methodology that includes a participatory process and social learning to ensure their successful implementation. By combining cost data, hydrological modelling and a bottom-up approach for three different European catchment areas (the Latvian Berze, the Swedish Helge and the German Selke rivers), the cost-effectiveness of 16 nutrient mitigation measures were analysed under current conditions as well as under selected scenarios for future climate and land-use changes. Fertiliser reduction, wetlands, contour ploughing and municipal wastewater treatment plants are the measures that remove nutrients with the highest cost-effectiveness in the respective case study context. However, the results suggest that the cost-effectiveness of measures not only depends on their design, specific location and the conditions of the surrounding area, but is also affected by the future changes the area may be exposed to. Climate and land-use changes do not only affect the cost-effectiveness of measures, but also shape the overall nutrient loads and potential target levels in a catchment.

Nutrient dynamics and retention in a vegetated drainage ditch receiving nutrient-rich sewage at low temperatures

Vegetated agricultural drainage ditches (VDs) are a relatively new best management practice for pesticide and nutrient mitigation that is receiving increasing global interest. However, VDs are seldom used during winter due to considerable deterioration of pollutants reduction efficiencies driven by low-temperature effects. Limited knowledge on the internal loading of nutrient in VDs due to vegetation decomposition calls for further evaluation. Here, we assessed plants growth characteristics and nutrient dynamics in a field-scale VD receiving nutrient-rich sewage and planted with the overwintering plants: Acorus gramineus, Myriophyllum aquaticum and Iris sibirica. Water purification performance showed average TN, NH4-N, NO3-N, TP and PO4-P reduction efficiencies of 44, 46, 43, 52 and 46%, respectively, over the winter period. Maximum reduction rates of TN and TP were 5.31 and 0.34 g−2 d−1, respectively. Of the total nutrient removal by plants of 5.37 × 103 kg N y−1 and 0.65 × 103 kg P y−1 from the VD system, A. gramineus contributed 65.7% and 72.1%, respectively. Nonetheless, substantial amounts of N and P retained within the aboveground biomass were released into the water column as ditch plant shoots decayed to deteriorate the water quality. All three species, A. gramineus, M. aquaticum and I. sibirica demonstrated considerable nutrient accumulation during winter and facilitated nutrient retention in the VD system. Consequently, they can be considered effective overwintering species of choice in VDs for purifying nutrient-rich water and potentially appropriate for vulgarizing elsewhere, particularly throughout the winter season.

A spatial model for nutrient mitigation potential of blue mussel farms in the western Baltic Sea

Worldwide, coastal and marine policies are increasingly aiming for environmental protection, and eutrophication is a global challenge, particularly impairing near-coastal marine water bodies. In this context, mussel mitigation aquaculture is currently considered an effective tool to extract nutrients from such water bodies. Mussel mitigation farming using longline systems with loops of collector material is a well-developed technology and considered promising in the western Baltic Sea. Besides several spatially limited field studies, a suitable spatial model for site-specific implementation is still lacking. In this study, we present a modular spatial model, consisting of a spatial and temporal habitat factor model (Module 1), blue mussel growth model (Module 2), mussel farm model (Module 3), and an avoidance of food limitation model (Module 4). The modules integrate data from in situ monitoring, mussel growth experiments, and eco-physiological modelling for the western Baltic Sea, to estimate spatially explicit nutrient reduction potentials. The model is flexible with respect to farm setups and harvest times and considers natural variability, model uncertainty, and required hydrodynamics. Modelling results proved valid at all scales and modules, and point out key areas for efficient mussel mitigation farms in Danish, German and Swedish areas. Modelled long-term mean mitigation potentials for harvest in November reach up to 0.88 tN/ha and 0.05 tP/ha for a farm setup using 2 m depth-range of the water column and 3.0 tN/ha and 0.17 tP/ha using up to 8 m, respectively. For Danish water bodies, we demonstrate that in efficient areas, mitigation farms (18.8 ha, 90 km collector substrate in loops with 2 m depth-range) required <3.6% of the space to extract the target nitrogen loads for good ecological status. The developed approach could prove valuable for implementing environmental policies in aquatic systems, e.g. in situ nutrient mitigation, aquaculture spatial planning, and habitat suitability mapping.

Diversity or Redundancy in Leaf Physiological and Anatomical Parameters in a Species Diverse, Bottomland Hardwood Forest?

Research Highlights: Bottomland hardwood forests exhibit seasonal flooding, are species diverse, and provide numerous ecosystem services including floodwater storage, wildlife habitat and nutrient mitigation. However, data are needed to adequately predict the potential of individual species to achieve these services. Background and Objectives: In bottomland hardwood forests, increasing tree species richness may increase functional diversity unless species exhibit an overlap in physiological functioning. Therefore, the objectives of this study were to (1) compare physiological and anatomical leaf parameters across species, (2) determine if leaf anatomical and nutrient properties were correlated with physiological functioning, (3) determine intra-species variability in leaf stomatal properties and determine how whole crown metrics compare with leaves measured for gas exchange and (4) measure soil nitrogen for evidence of denitrification during inundation periods. Materials and Methods: We measured gas exchange, leaf nutrients and anatomical properties in eight bottomland hardwood species including Carya ovata, Fraxinus pennsylvanica, Quercus michauxii, Quercus nigra, Quercus pagoda, Quercus phellos, Ulmus alata and Ulmus americana. Additionally, we quantified soil ammonium and nitrate content during winter inundated conditions to compare with non-inundation periods. Results: We found that leaf-level water use parameters displayed greater variability and diversity across species than photosynthesis and leaf nitrogen parameters, but green ash and shagbark hickory exhibited generally high leaf N concentrations and similar physiological functioning. Elms and oaks displayed larger variability in leaf physiological functioning. Stomatal density was significantly correlated with photosynthetic capacity and tree-level water use and exhibited high intra-species variability. Conclusions: This bottomland hardwood forest contains more diversity in terms of water use strategies compared with nitrogen uptake, suggesting that differences in species composition will affect the hydrology of the system. Green ash and shagbark hickory exhibit higher leaf nitrogen concentrations and potential for nutrient mitigation. Finally, leaf anatomical parameters show some promise in terms of correlating with leaf physiological parameters across species.

Influence of nutrient mitigation measures on the fractional export of watershed inputs in an urban watershed.

Enhanced nutrient inputs due to human activities have been noted as a significant driving force for riverine nutrient exports which are responsible for the eutrophication issues in freshwaters. Current studies are mostly focused on the relationship between anthropogenic inputs and riverine exports, and little has been done to assess the role of nutrient mitigation measures in the fractional export of watershed nutrient inputs in urban regions. A highly urbanized watershed in Yun-Gui plateau of China, Lake Dianchi basin was studied as a case to assess the impact of nutrient mitigation measures on riverine nutrient exports. Based on net anthropogenic nitrogen and phosphorus inputs (NANI and NAPI, respectively) models, nutrient inputs from human activities in the basin from 1980 to 2015 were calculated, and the impact of nutrient mitigation measures were identified using a statistical model incorporating land use, precipitation, and temperature. Nutrient inputs from human action in the basin has increased rapidly, mainly from fertilizer application and food and feed imports. Enhanced riverine nutrient exports were found at the same time, and significantly correlated to nutrient inputs. The construction of water transfer projects and wastewater treatment plants in the basin has changed the controlling factors and processes of the fractional export of watershed nutrient inputs, which is weak in explanatory ability and eliminated the role of the land use. A modified model was established by incorporating the effect of water transfer projects and wastewater treatment plants, which showed a significant increase in model performance. The results from the modified model reveal that urban land percentage has become a positively driving force for the fractional export of watershed N and P inputs, and temperature a positive driving force for the fractional export of watershed N inputs while precipitation a negative driving force for the fractional export of watershed P inputs.

Phytoplankton responses to adaptive management interventions in eutrophic urban estuaries

Upstream anthropogenic perturbations can dramatically affect estuarine water quality, especially in small systems where water retention times are high. Management of these modified ecosystems often requires direct interventions to prevent detrimental long-term effects. The heavily urbanized and temporarily closed Zandvlei Estuary in South Africa has a long history of anthropogenic manipulation, and therefore acts as an ideal case-study to gauge reactive management practices. Continued deterioration of estuarine water quality and ecological functioning prompted the adoption of an adaptive management approach. Subsequent management interventions to increase salinity variability and nutrient removal included the (1) adoption of a mouth management plan, (2) regular harvesting of submerged vegetation, and (3) removal of flow obstructions. Physico-chemical and nutrient monitoring data (2010–2018) were assessed to document the response of phytoplankton to these interventions. Time-series analysis indicated an upward trend in salinity throughout the estuary. This corresponded with a temporal decline in phytoplankton biomass levels and was supported by model results that highlighted a strongly inverse relationship with salinity. The frequency of high-biomass events (>80 μg Chl-a l−1) also declined in each of the designated estuarine zones. In April 2012, an extensive harmful algal bloom (HAB) of Prymnesium parvum (Prymnesiophyceae) was recorded (~530 μg Chl-a l−1) in the estuary, culminating in hypoxic conditions (O2 < 2 mg l−1) and fish kills. However, the subsequent mechanical breaching of the mouth has prevented reoccurrences of P. parvum. Similarly, more saline conditions arising from increased marine connectivity reduced the abundance of the previously dominant Bacillariophyceae and Chlorophyceae classes. The overall improvement in water quality validates the efficacy of management interventions aimed at restoring and conserving ecosystem functionality. Yet, these efforts are a deviation from natural estuarine functioning and thus a ‘catchment to coast’ approach that incorporates upstream nutrient mitigation measures is needed to achieve sustainable long-term management objectives.

Nutrient release from fish cage aquaculture and mitigation strategies in Daya Bay, southern China

Finfish cage culture is the most predominant form of mariculture. The rapid expansion of fish cage culture systems has raised concerns about their environmental impact, such as nutrient release. In this study, for the first time, we estimated the release of nitrogen (N) and phosphorus (P) from fish cage culture in Daya Bay, southern China, by constructing N and P budget models based on a mass balance principle. In addition, the contribution and importance of nutrients from fish culture and other nutrient sources, including submarine groundwater discharge, benthic sediments, local rivers, and atmospheric deposition were assessed. The annual amount of N and P released from fish cage culture was 205.6 metric tons (hereafter tons) of N and 39.2 tons of P, including 142.7 tons of dissolved inorganic nitrogen (DIN) and 15.1 tons of dissolved inorganic phosphorus (DIP). Among the analyzed nutrient sources, the contributions of DIN and DIP from fish culture were 7.0% and 2.7%, respectively. For cages consuming conventional trash fish, 142 kg of N and 26 kg of P were released into the environment per ton of fish products, much higher than the values (72 kg N and 17.3 kg P) for cages using formulated feed. In fish culture, the dissolved nutrients were more N rich, but the particulate nutrients were more P rich. The ratio of cage-derived N and P was 21.1, higher than the ratio of coastal seawater (27.1), indicating that cage culture may also impact the local nutrient forms around farming regions. Oyster cultivation and harvest removed 126.3 tons of N and 35.1 tons of P from of the bay. Replacing trash fish with formulated feed and co-culturing of nutrient extractive species (e.g., bivalves, macroalgae) and deposit-feeding species (e.g., sea cucumber) in fish culture zones can be efficient nutrient mitigation strategies.

Agricultural Water Quality in Cold Environments

Agricultural Water Quality in Cold Environments

Mussel production as a nutrient mitigation tool for improving marine water quality

Mussel production as a nutrient mitigation tool for improving marine water quality

Comparing the network structure and resilience of two benthic estuarine systems following the implementation of nutrient mitigation actions

The structure and resilience of benthic communities in coastal and estuarine ecosystems can be strongly affected by human mediated disturbances, such as nutrient enrichment, often leading to changes in a food webs function. In this study, we used the Ecopath model (EwE) to examine two case studies where deliberate management actions aimed at reducing nutrient pollution and restoring ecosystems resulted in ecological recovery. Five mass-balanced models were developed to represent pre and post-management changes in the benthic food web properties of the Tamar (1990, 1992, 2005) and Eden (1999, 2015) estuarine systems (UK). The network functions of interest were measures related to the cycling of carbon, nutrients and the productivity of the systems. Specific attention was given to the trophic structure and cycling pathways within the two ecosystems. The network attribute of ascendency was also examined as a proxy for resilience and used to define safe system-level operating boundaries. The results of the resilience metrics ascendancy (A) and its derivatives capacity (C) and overhead (O) indicate that both systems were more resilient and had higher resistance to potential stressors under low nutrient conditions. The less perturbed networks also cycled material more efficiently, according to Finns cycling index (CI), and longer cycling path lengths were indications of less stressed systems. Relative Ascendency (A/C) also proved useful for comparing estuarine systems of different sizes, suggesting the Tamar and Eden systems network structures have remained within their pre-defined “safe operating zones”. Overall, this analysis presents justification that efforts to reduce nutrient inputs into the Tamar and Eden estuaries have had a positive effect on the trophic networks of each system. Moreover, the consensuses of the network indicators in both systems suggest ecological network analysis (ENA) to be a suitable methodology to compare the recovery patterns of ecosystems of different sizes and complexity.

Measuring carbon and nitrogen bioassimilation, burial, and denitrification contributions of oyster reefs in Gulf coast estuaries

The eastern oyster (Crassostrea virginica) and the reefs they create provide significant ecosystem services. This study measured their possible role in nutrient mitigation through bioassimilation, burial, and oyster-mediated sediment denitrification in near-shore shallow water ( 1 m water depth) oyster reefs in Louisiana. Nitrogen (N) and carbon (C) in shell and tissue differed by oyster reproductive status, size, and habitat type. Changes in tissue percent N and C post-spawning combined with significant reductions in tissue dry weight from the release of gametes, resulted in 20 and 46% reductions in tissue N and C load (mg), respectively, for a 100-mm oyster. Oyster reefs did not enhance burial rates, with burial range rates estimated at 1.4–2.6 g N m−2 year−1, and 26.9–43.8 g C m−2 year−1. Closed-system ex situ incubations indicated net denitrification in all habitat types studied, with the highest rates exceeding 600 µmol N m−2 h−1 during the summer, but no enhancement attributable to oyster reefs specifically. Within the highly productive, organic-rich wetland complex systems of coastal Louisiana, oyster reefs were not associated with enhanced denitrification, likely due to the organic-rich setting, and redundant supplies of organic nitrogen and carbon from adjacent marshes. Context remains critical in determining ecosystem provision of habitats, and efforts to extrapolate and predict nitrogen removal across locations necessitates consideration of local conditions. Considering the large extent of reefs and oyster production across coastal Louisiana, oyster habitats may still contribute to N and C mitigation, but their unique contribution likely comes from bioassimilation, and removal of the oysters from the system.

Using dissolved organic matter fluorescence to identify the provenance of nutrients in a lowland catchment; the River Thames, England

Catchment based solutions are being sought to mitigate water quality pressures and achieve multiple benefits but their success depends on a sound understanding of catchment functioning. Novel approaches to monitoring and data analysis are urgently needed. In this paper we explore the potential of river water fluorescence at the catchment scale in understanding nutrient concentrations, sources and pathways. Data were collected from across the River Thames basin from January 2012 to March 2015.Analysing emission excitation matrices (EEMs) using both PARAFAC and optimal area averaging produced consistent results for humic-like component 1 and tryptophan-like component 4 in the absence of a subset of samples that exhibited an unusual peak; illustrating the importance of inspecting the entire EEM before using peak averaging methods. Strong relationships between fluorescence components and dissolved organic carbon (DOC), soluble reactive phosphorus (SRP), and ammonium clearly demonstrated its potential, in this study basin, as a field based surrogate for nutrients. Analysing relationships between fluorescence, catchment characteristics and boron from across the basin enabled new insights into the provenance of nutrients. These include evidence for diffuse sources of DOC from near surface hydrological pathways (i.e. soil horizons); point source inputs of nutrients from sewage effluent discharges; and diffuse contributions of nutrients from agriculture and/or sewage (e.g. septic tanks).The information gained by broad scale catchment wide monitoring of fluorescence could support catchment managers in (a) prioritising subcatchments for nutrient mitigation; (b) providing information on relative nutrient source contributions; and (c) providing evidence of the effectiveness of investment in pollution mitigation measures. The collection of high resolution fluorescence data at the catchment scale and, in particular, over shorter event timescales would complement broad scale assessments by enhancing our hydro-biogeochemical process understanding.

Challenges and Opportunities With On-Farm Research: Total and Soluble Reactive Stream Phosphorus Before and After Implementation of a Cattle-Exclusion, Riparian Buffer

Many nutrient mitigation best management practices (BMP) are promoted by state and federal agencies to protect water quality from animal agriculture. The measured effectiveness of these is highly variable in the research literature. Here, we establish pre- and post-BMP monitoring to evaluate the effectiveness of fencing out cattle from the riparian zone on water quality, specifically, phosphorus (P) loads and concentrations. We collected water samples year-round both before and after a cattle exclusion was established at a small mixed dairy and beef cattle pasture where cattle have historically grazed with unrestricted access to first and second order streams, and analyzed for soluble reactive and total P. Immediately after fence construction, we observed a significant reduction in total P in the stream but not in soluble reactive P. We also observed the development of new runoff source areas and short-circuiting of the riparian buffer as well as repeated presence of cows in the fenced-out area, all of which may diminish the potential effectiveness of this practice. Because BMPs will perform uniquely given climate and landscape position and how managers maintain them, we suggest the need for more nuanced guidance for future BMP designs to ensure successful outcomes.

A linked land-sea modeling framework to inform ridge-to-reef management in high oceanic islands.

Declining natural resources have led to a cultural renaissance across the Pacific that seeks to revive customary ridge-to-reef management approaches to protect freshwater and restore abundant coral reef fisheries. Effective ridge-to-reef management requires improved understanding of land-sea linkages and decision-support tools to simultaneously evaluate the effects of terrestrial and marine drivers on coral reefs, mediated by anthropogenic activities. Although a few applications have linked the effects of land cover to coral reefs, these are too coarse in resolution to inform watershed-scale management for Pacific Islands. To address this gap, we developed a novel linked land-sea modeling framework based on local data, which coupled groundwater and coral reef models at fine spatial resolution, to determine the effects of terrestrial drivers (groundwater and nutrients), mediated by human activities (land cover/use), and marine drivers (waves, geography, and habitat) on coral reefs. We applied this framework in two ‘ridge-to-reef’ systems (Hā‘ena and Ka‘ūpūlehu) subject to different natural disturbance regimes, located in the Hawaiian Archipelago. Our results indicated that coral reefs in Ka‘ūpūlehu are coral-dominated with many grazers and scrapers due to low rainfall and wave power. While coral reefs in Hā‘ena are dominated by crustose coralline algae with many grazers and less scrapers due to high rainfall and wave power. In general, Ka‘ūpūlehu is more vulnerable to land-based nutrients and coral bleaching than Hā‘ena due to high coral cover and limited dilution and mixing from low rainfall and wave power. However, the shallow and wave sheltered back-reef areas of Hā‘ena, which support high coral cover and act as nursery habitat for fishes, are also vulnerable to land-based nutrients and coral bleaching. Anthropogenic sources of nutrients located upstream from these vulnerable areas are relevant locations for nutrient mitigation, such as cesspool upgrades. In this study, we located coral reefs vulnerable to land-based nutrients and linked them to priority areas to manage sources of human-derived nutrients, thereby demonstrating how this framework can inform place-based ridge-to-reef management.

Importance of nitrate reduction in benthic carbon mineralization in two eutrophic estuaries: Modeling, observations and laboratory experiments

Estuaries are important nutrient filters between rivers and coastal zones. However, the quantification of the nutrient mitigation capacity related to benthic diagenesis is still poorly quantified. In this paper, we investigated carbon mineralization and the contribution of benthic nitrate reduction in two macrotidal eutrophic estuaries (Elorn and Aulne, Brittany, France) during winter and spring. These anthropized estuaries exhibited large variations of bottom water nitrate concentrations from very high values in upstream waters (up to 500 μM) to low values downstream (andlt; 10 μM). Bottom water oxygen concentrations presented small gradients compared to nitrate concentrations gradients resulting in large variation in nitrate to oxygen ratios NOx −/O2 between downstream and upstream (0.03–1.6). We combined the use of diagenesis modeling with field data (porosity, organic carbon and nitrogen, pore water profiles of dissolved oxygen, nitrogen, iron, manganese and sulfide concentrations, published in Khalil et al., 2013) and experimentally-determined nitrate reduction rates, in order to investigate the different organic carbon mineralization pathways in these estuarine sediments including denitrification and the contribution of benthic nitrate reduction to the estuarine N budget. Overall a good agreement between pore water data (organic carbon, oxygen, nitrate and ammonium) and model simulations was observed. The modeled organic matter mineralization rates were high in the upstream estuary and low in the saline estuary for the two estuaries Aulne and Elorn. This decrease may be related to the dilution and the trapping of allochtonous organic matter in estuarine sediments and its subsequent recycling in the upper estuary. Organic carbon mineralization rates were higher in the Elorn than in the Aulne estuary, which is most likely related to the labile character of the organic matter from urban origin exported from the Elorn watershed. The contribution of nitrate reduction to the total mineralization was generally high in upstream sediments (15–35%) of both Aulne and Elorn estuaries and decreased consistently downstream to 5–10%. The relative large contribution of nitrate reduction to organic matter degradation was to a large extent related to high bottom water nitrate concentrations that fueled 37–78% of total nitrate reduction in the upstream part of the estuaries. Overall, the reduction of bottom water nitrate by denitrification to N2 represented 3–13% of the river flux of nitrate in these estuaries in winter and spring, and could reach ~ 50% during summer. These results highlight that nitrate reduction in the sediment attenuate the high river nitrate flux, despite the huge quantities of anthropogenic nitrate discharged by the two rivers to the estuaries.

Management to Insulate Ecosystem Services from the Effects of Catchment Development

Natural ecosystems provide amenity to human populations in the form of ecosystem services. These services are grouped into four broad categories: provisioning – food and water production; regulating – control of climate and disease; supporting – crop pollination; and cultural – spiritual and recreational benefits. Aquatic systems provide considerable service through the provision of potable water, fisheries and aquaculture production, nutrient mitigation and the psychological benefits that accrue from the aesthetic amenity provided from lakes, rivers and other wetlands. Further, littoral and riparian ecosystems, and aquifers, protect human communities from sea level encroachment, and tidal and river flooding. Catchment and water development provides critical resources for human consumption. Where these provisioning services are prioritized over others, the level and quality of production may be impacted. Further, the benefits from these provisioning services comes with the opportunity cost of diminishing regulating, supporting and cultural services. This imbalance flags concerns for humanity as it exceeds recognised safe operating spaces. These concepts are explored by reference to long term records of change in some of the world’s largest river catchments and lessons are drawn that may enable other communities to consider the balance of ecosystems services in natural resource management.

Influence of land use on the persistence effect of riverine phosphorus

AbstractThe persistence effect contribution of legacy nutrients is often cited as a reason for little or no improvement in water quality following extensive implementation of watershed nutrient mitigation actions, yet there is limited knowledge concerning factors influencing this response, often called the “persistence effect.” Here, we adopted detrended fluctuation analysis and Spearman analysis methods to assess the influence of land use on the watershed phosphorus (P) persistence effect, using monthly water quality records during 2010–2016 in 13 catchments within a drinking water reservoir watershed in eastern China. Detrended fluctuation analysis was used to calculate the Hurst exponent α to assess watershed legacy P characteristics (α ≈ 0.5, α &gt; 0.5, and α &lt; 0.5 indicate white noise, persistence, and anti‐persistence, respectively). Results showed weak to strong P persistence (0.60–0.81) in the time series of riverine P in the 13 catchments. The Hurst exponent α had negative relationships with agricultural land (R = −.47, p = .11) and developed land (R = −.67, p = .01) and a positive relationship with forest land cover (R = .48, p = .10). The persistence effect of riverine P was mainly determined by retention ability (biogeochemical legacy) and migration efficiency (hydrological legacy). A catchment with strong retention capacity (e.g., biomass uptake/storage and soil PO4 sorption) and low migration efficiency results in a stronger persistence effect for riverine P. In practice, source control is more effective in catchments with weak persistence, whereas sink control (e.g., riparian buffers and wetlands) is preferred in catchments with strong persistence effects.