Balancing macronutrient stoichiometry to alleviate eutrophication.

Reactive nitrogen (N) and phosphorus (P) inputs to surface waters modify aquatic environments, affect public health and recreation. Source controls dominate eutrophication management, whilst biological regulation of nutrients is largely neglected, although aquatic microbial organisms have huge potential to process nutrients. The stoichiometric ratio of organic carbon (OC) to N to P atoms should modulate heterotrophic pathways of aquatic nutrient processing, as high OC availability favours aquatic microbial processing. Heterotrophic microbial processing removes N by denitrification and captures N and P as organically-complexed, less eutrophying forms. With a global data synthesis, we show that the atomic ratios of bioavailable dissolved OC to either N or P in rivers with urban and agricultural land use are often distant from a "microbial optimum". This OC-deficiency relative to high availabilities of N and P likely overwhelms within-river heterotrophic processing. We propose that the capability of streams and rivers to retain N and P may be improved by active stoichiometric rebalancing. Although autotrophic OC production contributes to heterotrophic rates substantial control on nutrient processing from allochthonous OC is documented for N and an emerging field for P. Hence, rebalancing should be done by reconnecting appropriate OC sources such as wetlands and riparian forests that have become disconnected from rivers concurrent with agriculture and urbanisation. However, key knowledge gaps require research prior to the safe implementation of this approach in management: (i) to evaluate system responses to catchment inputs of dissolved OC forms and amounts relative to internal production of autotrophic dissolved OC and aquatic and terrestrial particulate OC and (ii) evaluate risk factors in anoxia-mediated P desorption with elevated OC scenarios. Still, we find stoichiometric rebalancing through reconnecting landscape beneficial OC sources has considerable potential for river management to alleviate eutrophication, improve water quality and aquatic ecosystem health, if augmenting nutrient source control.

A cloud based tool for knowledge exchange on local scale flood risk.

There is an emerging and urgent need for new approaches for the management of environmental challenges such as flood hazard in the broad context of sustainability. This requires a new way of working which bridges disciplines and organisations, and that breaks down science-culture boundaries. With this, there is growing recognition that the appropriate involvement of local communities in catchment management decisions can result in multiple benefits. However, new tools are required to connect organisations and communities. The growth of cloud based technologies offers a novel way to facilitate this process of exchange of information in environmental science and management; however, stakeholders need to be engaged with as part of the development process from the beginning rather than being presented with a final product at the end. Here we present the development of a pilot Local Environmental Virtual Observatory Flooding Tool. The aim was to develop a cloud based learning platform for stakeholders, bringing together fragmented data, models and visualisation tools that will enable these stakeholders to make scientifically informed environmental management decisions at the local scale. It has been developed by engaging with different stakeholder groups in three catchment case studies in the UK and a panel of national experts in relevant topic areas. However, these case study catchments are typical of many northern latitude catchments. The tool was designed to communicate flood risk in locally impacted communities whilst engaging with landowners/farmers about the risk of runoff from the farmed landscape. It has been developed iteratively to reflect the needs, interests and capabilities of a wide range of stakeholders. The pilot tool combines cloud based services, local catchment datasets, a hydrological model and bespoke visualisation tools to explore real time hydrometric data and the impact of flood risk caused by future land use changes. The novel aspects of the pilot tool are; the co-evolution of tools on a cloud based platform with stakeholders, policy and scientists; encouraging different science disciplines to work together; a wealth of information that is accessible and understandable to a range of stakeholders; and provides a framework for how to approach the development of such a cloud based tool in the future. Above all, stakeholders saw the tool and the potential of cloud technologies as an effective means to taking a whole systems approach to solving environmental issues. This sense of community ownership is essential in order to facilitate future appropriate and acceptable land use management decisions to be co-developed by local catchment communities. The development processes and the resulting pilot tool could be applied to local catchments globally to facilitate bottom up catchment management approaches.

Reprint of: Assessment of the use of sediment fences for control of erosion and sediment phosphorus loss after potato harvesting on sloping land.

In humid temperate areas, after harvest of potatoes, it is difficult to prevent soil erosion and diffuse pollution. In some autumn weather conditions, in-field mitigation such as cultivation or sowing are not possible, while edge of field measures can be costly and inflexible. We have assessed the potential of modified sediment fences, widely used on building sites, for erosion mitigation post-harvest of potato crops. Field scale assessments were conducted on fields in the Lunan catchment, eastern Scotland. Sediment retention was estimated by two methods: a topographic survey method using a hand held Real Time Kinematic Global Positioning System (RTK-GPS), and direct measurement of sediment depth using a graduated cane. In the 2010/11 trial the main fence comprised 70 m of entrenched fine mesh (0.25 mm) and coarser mesh (4mm) fabric pinned to a contour fence near the base of the field. This retained an estimated 50.9 m(3) (80.2 tonnes) of sediment, with weighted mean total P (TP) content of 0.09 % in the<2mm soil fraction. In the 2011/12 trial, the main 146 m fence was of intermediate mesh size (1.2mm). The fence was partitioned into nine upslope plots, with 3 replicates of each of 3 cultivation methods: T1 (full grubbing--a light, tined cultivator), T2 (partial grubbing) and T3 (no grubbing). Average plot slopes ranged from 9.9 to 11.0 %. The amounts of TP accumulating as sediment at the fences were: 9.3 (sd=7.8), 11.8 (sd=10.2) and 25.7 (sd=5.8)kg P/ha of upslope plot for the T1, T2 and T3 treatments respectively.

Assessment of the use of sediment fences for control of erosion and sediment phosphorus loss after potato harvesting on sloping land.

In humid temperate areas, after harvest of potatoes, it is difficult to prevent soil erosion and diffuse pollution. In some autumn weather conditions, in-field mitigation such as cultivation or sowing are not possible, while edge of field measures can be costly and inflexible. We have assessed the potential of modified sediment fences, widely used on building sites, for erosion mitigation post-harvest of potato crops. Field scale assessments were conducted on fields in the Lunan catchment, eastern Scotland. Sediment retention was estimated by two methods: a topographic survey method using a hand held Real Time Kinematic Global Positioning System (RTK-GPS), and direct measurement of sediment depth using a graduated cane. In the 2010/11 trial the main fence comprised 70 m of entrenched fine mesh (0.25 mm) and coarser mesh (4mm) fabric pinned to a contour fence near the base of the field. This retained an estimated 50.9 m(3) (80.2 tonnes) of sediment, with weighted mean total P (TP) content of 0.09 % in the<2mm soil fraction. In the 2011/12 trial, the main 146 m fence was of intermediate mesh size (1.2mm). The fence was partitioned into nine upslope plots, with 3 replicates of each of 3 cultivation methods: T1 (full grubbing--a light, tined cultivator), T2 (partial grubbing) and T3 (no grubbing). Average plot slopes ranged from 9.9 to 11.0 %. The amounts of TP accumulating as sediment at the fences were: 9.3 (sd = 7.8), 11.8 (sd = 10.2) and 25.7 (sd = 5.8)kg P/ha of upslope plot for the T1, T2 and T3 treatments respectively.

Biodegradability of natural dissolved organic matter collected from a UK moorland stream.

The fate of dissolved organic matter (DOM) exported from headwaters is a large uncertainty in global carbon models and catchment biogeochemical process understanding. We examined the biodegradability of stream DOM collected during different flow conditions (n = 12) from a heather-dominated moorland headwater in NE Scotland. Freeze-dried DOM isolates were characterised, re-dissolved to 10 mg C L(-1), inoculated with indigenous stream sediment microbes and incubated, with and without added nutrients, to assess decomposition rates at different times up to 41 days. Biodegradable DOM ranged from 5.0 to 19% of the total transported DOM, representing 8.54 kg C ha(-1) yr(-1) (11.1% of the total DOC flux, calculated as 77.2 ± 39.0 kg C ha(-1) yr(-1)). No simple patterns with flow rate were apparent but accumulated antecedent rainfall, specific UV absorbance of DOM and (15)N content were significant predictors of the proportion of organic matter decomposed. In headwater streams draining organic-rich catchments, in-stream DOM decomposition processes act as a secondary control on the spatial variability of carbon species, and are important for establishing accuracy of aquatic carbon fluxes and cycling budgets. Moreover, biologically-mediated DOM decomposition represents a net 'climate forcing effect' via the soil-stream-atmosphere pathway, drives downstream ecosystem metabolism and should be incorporated in carbon predictive modelling and ecosystem process studies.

The Tarland Catchment Initiative and its effect on stream water quality and macroinvertebrate indices.

The Tarland Catchment Initiative is a partnership venture between researchers, land managers, regulators, and the local community. Its aims are to improve water quality, promote biodiversity, and increase awareness of catchment management. In this study, the effects of buffer strip installations and remediation of a large septic tank effluent were appraised by water physico-chemistry (suspended solids, NO, NH, soluble reactive P) and stream macroinvertebrate indices used by the Scottish Environmental Protection Agency. It was done during before and after interventions over an 8-yr period using a paired catchment approach. Because macroinvertebrate indices were previously shown to respond negatively to suspended solid concentrations in the study area, the installation of buffer strips along the headwaters was expected to improve macroinvertebrate scores. Although water quality (soluble reactive P, NH) improved downstream of the septic tank effluent after remediation, there was no detectable change in macroinvertebrate scores. Buffer strip installations in the headwaters had no measurable effects (beyond possible weak trends) on water quality or macroinvertebrate scores. Either the buffer strips have so far been ineffective or ineffectiveness of assessment methods and sampling frequency and time lags in recovery prevent us detecting reliable effects. To explain and appreciate these constraints on measuring stream recovery, continuous capacity building with land managers and other stakeholders is essential; otherwise, the feasibility of undertaking sufficient management interventions is likely to be compromised and projects deemed unsuccessful.

The biogeochemical reactivity of suspended particulate matter at nested sites in the Dee basin, NE Scotland.

Variation in the organic matter content associated with suspended particulate matter (SPM) is an often overlooked component of carbon cycling within freshwater riverine systems. The potential biogeochemical reactivity of particulate organic carbon (POC) that affect its interactions and fate, i.e. respired and lost to the atmosphere along river continua or ultimately exported to estuarine and oceanic pools was assessed. Eleven contrasting sites draining nested catchments (5-1837 km(2)) in the River Dee basin, NE Scotland were sampled during summer 2008 to evaluate spatio-temporal variations in quantity and quality (biogeochemical reactivity) of SPM during relatively low flow conditions. Mean SPM concentrations increased from 0.21 to 1.22 mg L(-1) between the uppermost and lowest mainstem sites. Individually, POC concentrations ranged from 0.08 to 0.55 mg L(-1) and accounted for ca. 3-15% of total aqueous organic carbon transported. The POC content was partitioned into autotrophic (2.78-73.0 mg C g(-1) SPM) and detrital (119-388 mg C g(-1) SPM) biomass carbon content. The particulate respired CO(2)-C as a % of the total carbon associated with SPM, measured by MicroResp™ over 18 h, varied in recalcitrance from 0.49% at peat-dominated sites to 3.20% at the lowermost mainstem site. Significant (p<0.05) relationships were observed between SPM biogeochemical reactivity measures (% respired CO(2)-C; chlorophyll α; bioavailable-phosphorus) and arable and improved grassland area, associated with increasing biological productivity downstream. Compositional characteristics and in-stream processing of SPM appear to be related to contributory land use pressures, that influence SPM characteristics and biogeochemistry (C:N:P stoichiometry) of its surrounding aqueous environment. As moorland influences declined, nutrient inputs from arable and improved grasslands increasingly affected the biogeochemical content and reactivity of both dissolved and particulate matter. This increases the potential for recycling of the organic matter that is either transported from upstream or entering further along the riverine continuum.

River phosphorus cycling: separating biotic and abiotic uptake during short-term changes in sewage effluent loading.

Medium to small scale point sources continue to threaten river ecosystems through P loadings. The capacity and timescales of within-river processing and P retention are a major factor in how rivers respond to, and protect downstream ecosystems from, elevated concentrations of soluble reactive P (SRP). In this study, the bio-geochemical response of a small river (approximately 40 km(2) catchment area) was determined before, during and after exposure to a fourteen day pulse of treated sewage effluent using an upstream reach as a control. A wide array of approaches (batch and column simulations to in-situ whole stream metabolism) allowed independent comparison and quantification, of the relative contribution of abiotic and biotic processes in-river P cycling. This enabled, for the first time, separating the relative contributions of algae, bacteria and abiotic sorption without the use of labelled P (radioisotope). An SRP mass balance showed that the ecosystem switched from a P sink (during effluent inputs) to a P source (when effluent flow ceased). However, 65-70% of SRP was retained during the exposure time and remained sequestered two-weeks after-effluent flow ceased. Batch studies treated with biocide gave unrealistic results, but P uptake rates derived by other methods were highly comparable. Downstream of the effluent input, net P uptake by algae, bacteria and sediment (including the biofilm polysaccharide matrix) were 0.2 (+/-0.1), 0.4 (+/-0.3), and 1.0 (+/-0.9) mmol m(-2) day(-1) during effluent exposure. While autotrophic production did not respond to the effluent exposure, heterotrophic production increased by 67% relative to the control and this translated into a 50% increase in biological P uptake rate. Therefore, both biological and abiotic components of stream ecosystems uptake P during exposure to treated sewage effluent P inputs, and maintain a long 'memory' of this input in terms of P storage for considerable timescales after loading.

Interactions of land use and dynamic river conditions on sorption equilibria between benthic sediments and river soluble reactive phosphorus concentrations.

Within-river cycling of P is a crucial link between catchment pollution sources and the resulting ecological impacts and integrates the biogeochemistry and hydrodynamics of river systems. This study investigates benthic sediment P sorption in relation to river soluble reactive phosphorus (SRP) concentrations during high- to low-flow changes in a major mixed land use river system in NE Scotland. We hypothesised that sediments comprised P sinks during moderate to higher flows but became P saturated with loss of buffering function during prolonged baseflow. Sediment characteristics were evaluated and equilibrium P concentrations (EPC(0)) calculated using a standardised batch adsorption method (EPC(0) values 0.04-1.75 micromol Pl(-1)). Pollution-impacted tributaries (32-69% catchment agricultural land cover) had increased SRP concentrations (0.19-2.62 micromol Pl(-1)) and maintained EPC(0)SRP values during summer baseflow so that sediments were indicated as P sources. This deviation from a geochemical sediment-water P equilibrium was attributed to biological accumulation of P from the water column into the sediments. In particular, large stores of sediment P accumulated in main stem reaches below agricultural tributaries and this may be consequential for sensitive downstream ecosystems. Hence, biogeochemical processes at the river bed may strongly influence river SRP cycling between geochemical and biotic pools. The nature of this internal reservoir of river P and its ecosystem interactions needs better understanding to enable best results to be attained from catchment mitigation actions designed to maintain/improve ecological status under the Water Framework Directive.

River sediments provide a link between catchment pressures and ecological status in a mixed land use Scottish River system.

This study evaluates water quality, suspended and bed sediment, ecological and catchment land use data for 13 catchments of the mixed land use River Dee, NE Scotland, where pollution point sources are limited. Samples were collected at key times of biological activity (early and late summers). Mean river water concentrations were smaller in main stem and upland sites and greater in tributaries where agricultural pressures were greater and were 2-41 microgPO(4)-Pl(-1), 8-58 microg total dissolved Pl(-1) and 1-6 mg l(-1) of suspended particulate matter (SPM). SPM was 7-372 times enriched in biologically available P (BAP; determined using an FeO paper strip method) and 2-122 times in organic C relative to bed sediments. Ratios in river water concentrations of BAP attributed to the SPM (0.1-1.0 microgPl(-1)) to PO(4)-P had the greatest range at baseflow (0.01-0.80) with larger values for low land use intensity catchments. During May chlorophyll a concentrations were related to SPM BAP (p<0.001), but later in summer to PO(4)-P, and there was a corresponding change in the organic composition of SPM observed by IR spectroscopy. SPM concentrations and SPM BAP were better related to intensive grassland land use (p<0.001) than was PO(4)-P concentration (p<0.01) and also predicted abundances of filter feeding macroinvertebrates (p<0.001). Within this river system SPM quantity and composition proved to be an indicator of river biogeochemical functioning and requires further investigation as a potentially sensitive monitoring tool and to increase our understanding of chemical ecological links.