Biogeochemical and hydrological controls on phosphorus transport in a floodplain fen.

This study investigates the biogeochemical controls on the release of phosphorus (P) from riparian wetland sediments to solution, and the subsequent delivery of P to receiving waters. The research was conducted at Strumpshaw Fen, a riparian wetland in the floodplain of the River Yare in the UK. Novel mesocosm work identifies the reductive-dissolution of iron-bound P as the dominant control on P release to solution. The timing of P release to pore water and surface water is also influenced by the concentration of nitrate-nitrogen in floodwater, because redox potential is poised above the level necessary for the reduction 0 f ferric iron whilst nitrate remains in solution. Field-based hydrochemical monitoring confirms the findings from laboratory mesocosm work on the controls on P release to solution, and indicates that P concentrations indicative of hyper eutrophic conditions may be established in the pore water and surface water of this riparian wetland. Sequential filtration establishes that the vast majority of the MRP fraction in 0.45 J.1m filtrates may be composed of free orthophosphate. An investigation of hydrological connectivity between the shallow peat and (i) the underlying mineral aquifer and (ii) the adjacent open-water network is used to indicate whether P in solution might be exported from the peat in large quantities. Reliable characterisation of the hydraulic conductivity (K) of the peat deposits at Strumpshaw Fen is achieved after a thorough evaluation of the piezometer technique, and the application of a novel laboratory-based method. K is found to be relatively high, indicating a potential for substantial flows of water between the near-surface peat and the ditch network at the site, given suitable hydraulic gradients. Field-based hydrological monitoring suggests that lateral exchanges between the peat and adjacent open-water bodies are more important than vertical exchanges between the peat and the underlying mineral aquifer. It is shown that the combination of P availability and hydrological connectivity between the peat and open water, will result in bioavailable P reaching the ditch network at Strumpshaw. In the light of these findings, riparian fen wetlands should not be assumed a priori to be 'protectors' of the chemical and ecological quality of receiving waters, but may in fact be sources for significant quantities of P that have the potential to be exported from the fen system

Public water supply is responsible for significant fluxes of inorganic nitrogen in the environment

Understanding anthropogenic disturbance of macronutrient cycles is essential for assessing risks facing ecosystems. For the first time, we quantified inorganic nitrogen (N) fluxes associated with abstraction, mains water leakage and transfers of treated water related to public water supply. In England, the mass of nitrate-N removed from aquatic environments by abstraction (ABS-NO3-N) was estimated to be 24.2 kt N/yr. This is equal to six times estimates of organic N removal by abstraction, 15 times in-channel storage of organic N and 30 times floodplain storage of organic N. ABS-NO3-N is also between 3-39% of N removal by denitrification in the hydrosphere. Mains water leakage of nitrate-N (MWL-NO3-N) returns 3.62 kt N/yr to the environment, equating to approximately 15% of ABS-NO3-N . In urban areas, MWL-NO3-N can represent up to 20% of total N inputs. MWL-NO3-N is predicted to increase by up to 66% by 2020 following implementation of treated water transfers. ABS-NO3-N and MWL-NO3-N should be considered in future assessments of N fluxes, in order to accurately quantify anthropogenic disturbances to N cycles. The methodology we developed is transferable, using widely-available datasets and could be used to quantify N fluxes associated with public water supply across the world

New approaches to enhance pollutant removal in artificially aerated wastewater treatment systems

Freshwater ecosystems sustain human society through the provision of a range of services. However, the status of these ecosystems is threatened by a multitude of pressures, including point sources of wastewater. Future treatment of wastewater will increasingly require new forms of decentralised infrastructure. The research reported here sought to enhance pollutant removal within a novel wastewater treatment technology, based on un-planted, artificially aerated, horizontal subsurface flow constructed wetlands. The potential for these systems to treat de-icer contaminated runoff from airports, a source of wastewater that is likely to grow in importance alongside the expansion of air travel and under future climate scenarios, was evaluated. A new configuration for the delivery of air to aerated treatment systems was developed and tested, based on a phased-aeration approach. This new aeration approach significantly improved pollutant removal efficiency compared to alternative aeration configurations, achieving > 90 % removal of influent load for COD, BOD5 and TOC. Optimised operating conditions under phased aeration were also determined. Based on a hydraulic retention time of 1.5 d and a pollutant mass loading rate of 0.10 kg d⁻¹ m⁻² BOD₅, > 95 % BOD5 removal, alongside final effluent BOD5 concentrations 800 mg L-1. Key controls on oxygen transfer efficiency within the aerated treatment system were also determined, revealing that standard oxygen transfer efficiency was inversely related to aeration rate between 1 L and 3 L min-1 and positively related to bed media depth between 1,500 mm and 3,000 mm. The research reported here highlights the potential for optimisation and subsequent widespread application of the aerated wetland technology, in order to protect and restore freshwater ecosystems and the services that they provide to human society

A multi-stable isotope framework to understand eutrophication in aquatic ecosystems

Eutrophication is a globally significant challenge facing aquatic ecosystems, associated with human induced enrichment of these ecosystems with nitrogen (N) and phosphorus (P). However, the limited availability of inherent labels for P and N has constrained understanding of the triggers for eutrophication in natural ecosystems and appropriate targeting of management responses. This paper proposes and evaluates a new multi-stable isotope framework that offers inherent labels to track biogeochemical reactions governing both P and N in natural ecosystems. The framework couples highly novel analysis of the oxygen isotope composition of phosphate (δ18OPO4) with dual isotope analysis of oxygen and N within nitrate (δ15NNO3, δ18ONO3) and with stable N isotope analysis in ammonium (δ15NNH4). The River Beult in England is used as an exemplar system for initial evaluation of this framework. Our data demonstrate the potential to use stable isotope labels to track the input and downstream fate of nutrients from point sources, on the basis of isotopic differentiation for both P and N between river water and waste water treatment work effluent (mean difference = +1.7‰ for δ18OPO4; +15.5‰ for δ15NNH4 (under high flow); +7.3‰ for δ18ONO3 and +4.4‰ for δ15NNO3). Stable isotope data reveal nutrient inputs to the river upstream of the waste water treatment works that are consistent with partially denitrified sewage or livestock sources of nitrate (δ15NNO3 range = +11.5 to +13.1‰) and with agricultural sources of phosphate (δ18OPO4 range = +16.6 to +19.0‰). The importance of abiotic and metabolic processes for the in-river fate of N and P are also explored through the stable isotope framework. Microbial uptake of ammonium to meet metabolic demand for N is suggested by substantial enrichment of δ15NNH4 (by 10.2‰ over a 100 m reach) under summer low flow conditions. Whilst the concentration of both nitrate and phosphate decreased substantially along the same reach, the stable isotope composition of these ions did not vary significantly, indicating that concentration changes are likely driven by abiotic processes of dilution or sorption. The in-river stable isotope composition and the concentration of P and N were also largely constant downstream of the waste water treatment works, indicating that effluent-derived nutrients were not strongly coupled to metabolism along this in-river transect. Combined with in-situ and laboratory hydrochemical data, we believe that a multi-stable isotope framework represents a powerful approach for understanding and managing eutrophication in natural aquatic ecosystems

Use of littoral algae to detect zones of nutrient enrichment in the littoral of an oligotrophic lake

The potential for using benthic algae to identify areas around the lake littoral that are potentially influenced by diffuse inputs of nutrients is considered through research based around Ennerdale Water in NW England. This is an oligotrophic lake with a highly sensitive population of Margalifera margalifera in the outflow river. Water chemistry, algal biomass, diatoms and macroalgae were studied at six points around the perimeter of the lake. Evidence of higher concentrations of dissolved nutrients along with alterations in the diatom and, to a lesser extent, macroalgae assemblages was found in the north-west corner of the lake. Algal biomass gave a more ambiguous signal, with local variations in biomass masked by stronger seasonal signals that determined the quantity of algae present at a site on any given date. These results demonstrate the potential for using benthic algae to generate more focussed data on the condition of a lake than is possible with the whole-lake assessments on which classifications are based

Mains water leakage: Implications for phosphorus source apportionment and policy responses in catchments

Effective strategies to reduce phosphorus (P)-enrichment of aquatic ecosystems require accurate quantification of the absolute and relative importance of individual sources of P. In this paper, we quantify the potential significance of a source of P that has been neglected to date. Phosphate dosing of raw water supplies to reduce lead and copper concentrations in drinking water is a common practice globally. However, mains water leakage (MWL) potentially leads to a direct input of P into the environment, bypassing wastewater treatment. We develop a new approach to estimate the spatial distribution and time-variant flux of MWL-P, demonstrating this approach for a 30-year period within the exemplar of the River Thames catchment in the UK. Our analyses suggest that MWL-P could be equivalent to up to c.24% of the P load entering the River Thames from sewage treatment works and up to c.16% of the riverine P load derived from agricultural non-point sources. We consider a range of policy responses that could reduce MWL-P loads to the environment, including incorporating the environmental damage costs associated with P in setting targets for MWL reduction, alongside inclusion of MWL-P within catchment-wide P permits