Implications For Nutrient Management Research Articles

Sedimentary mud and phaeophytin-a are reliable predictors of oxygen consumption and nitrogen turnover in the southern North Sea

Coastal systems are exposed to variable human uses and anthropogenic pressures, yet they provide valuable ecosystem services. Understanding the benthic processes in these systems is crucial for their effective management and conservation. This study investigates sediment characteristics as proxies for oxygen and nitrogen turnover in coastal, sandy, permeable sediments. We incubated sediment samples to quantify the turnover of ammonium and nitrate and analyzed various sediment properties to determine the most suitable predictors of sediment reactivity. Oxygen consumption rates and rates of ammonium and nitrate turnover strongly correlate with mud content and phaeophytin-a, which are identified as the best proxies for sediment reactivity. Ultimately, our data show that sediment nutrient recycling and turnover is intimately linked to spring primary production in the water column. In order to deduce reaction rates of oxygen, ammonium and nitrate from sediment properties, we provide linear regression coefficients and their uncertainties, enabling access to previous observations that would otherwise remain inaccessible due to missing data. This study provides insights for the development of benthic models that ultimately can be used to assess the impact of anthropogenic pressures on coastal systems. The findings have implications for nutrient management and monitoring in the German Bight, as an improved understanding of sediment reactivity allows for more appropriate and sustainable management and monitoring policies to be implemented.

Nutrient Sufficiency Ranges for Corn at the Early Growth Stage: Implications for Nutrient Management.

Growers rely on nutrient sufficiency ranges (NSRs) after plant tissue analysis to inform timely nutrient management decisions. The NSRs are typically established from survey studies across multiple locations, which could be confounded by several abiotic and biotic factors. We conducted field studies in 2020, 2021, and 2022 to validate the lower thresholds of the NSRs for corn (Zea mays) at the early growth stage as reported in the Southern Cooperative Series Bulletin #394. We induced various corn nutritional levels by making different nutrient application rates. If the NSRs are valid, samples within the same replication that satisfy the NSRs of all nutrients should have similar biomass accumulation. The results showed that the NSRs were not valid under the conditions tested. In total, 47.6% of the samples satisfied all the lower thresholds of the NSRs, and 25.4% of those samples had relative biomass <50%, with relative biomass even as low as 24.2% observed. Moreover, 9.6% of the total samples had P and Cu levels that failed to meet the lower threshold but still had relative biomass ≥75%. The findings highlight the sensitivity of corn to nutrient imbalance and the need to optimize nutrient diagnostic methods at the early growth stage.

Phosphorus Accumulation in Extracellular Polymeric Substances (EPS) of Colony-Forming Cyanobacteria Challenges Imbalanced Nutrient Reduction Strategies in Eutrophic Lakes.

Extracellular polymeric substances (EPS) are crucial for cyanobacterial proliferation; however, certain queries, including how EPS affects cellular nutrient processes and what are the implications for nutrient management in lakes, are not well documented. Here, the dynamics of cyanobacterial EPS-associated phosphorus (EPS-P) were examined both in a shallow eutrophic lake (Lake Taihu, China) and in laboratory experiments with respect to nitrogen (N) and phosphorus (P) availability. Results indicated that 40-65% of the total cyanobacterial aggregate/particulate P presented as EPS-P (mainly labile P and Fe/Al-P). Phosphorus-starved cyanobacteria rapidly replenished their EPS-P pools after the P was resupplied, and the P concentration in this pool was stable for long afterward, although the environmental P concentration decreased dramatically. A low-N treatment enhanced the EPS production alongside two-fold EPS-P accumulation (particularly labile P) higher than the control. Such patterns occurred in the lake where EPS and EPS-P contents were high under N limitation. EPS-P enrichment increased the P content in cyanobacteria; subsequently, it could hold the total P concentration higher for longer and make bloom mitigation harder. The findings outline a new insight into EPS functions in the P process of cyanobacterial aggregates and encourage consideration of both N and P reductions in nutrient management.

Contributions of external nutrient loading and internal cycling to cyanobacterial bloom dynamics in Lake Taihu, China: Implications for nutrient management

AbstractHarmful cyanobacterial blooms (CyanoHABs) are linked to increasing anthropogenic nitrogen (N) and phosphorus (P) inputs. However, CyanoHABs in many large lakes continue despite extensive abatement efforts, mostly focused on external P loading. Internal nutrient cycling can modify nutrient availability and limitation; thus, understanding the relative importance of external vs. internal nutrient loading is essential for developing effective mitigation strategies for CyanoHABs. We estimated long‐term nutrient budgets for Lake Taihu, China, from mass balance models using extensive monitoring of input and output nutrient data from 2005 to 2018 to quantify contributions from internal nutrient loading. The nutrient mass balance showed that 9% and 63% of annual external N and P inputs, respectively, were retained in the lake. Denitrification removed 54% of external N loading and can thus help explain rapid decreases in lake N concentrations and summer N limitation. Water columnregeneration can help sustain CyanoHABs over the short term and contributed 38–58% of potentialdemand for summer‐fall,Microcystis‐dominated blooms. Internal P release contributed 23–90% of CyanoHABs P demand, although Taihu was a net P sink on an annual scale. Our results show that internal nutrient cycling helps sustain CyanoHABs in Taihu, despite reductions in external nutrient inputs. Furthermore, N is leaving the lake faster than P, thereby creating persistent N limitation. Therefore, parallel reductions in external N loading, along with P, will be most effective in reducing CyanoHABs and accelerate the recovery process in this and other large, shallow lakes.

Contributions of external nutrient loading and internal cycling to cyanobacterial bloom dynamics in Lake Taihu, China: Implications for nutrient management

Contributions of external nutrient loading and internal cycling to cyanobacterial bloom dynamics in Lake Taihu, China: Implications for nutrient management

Dynamics of biomass and nutrient accumulation in rubber (Hevea brasiliensis) plantations established on two soil types: Implications for nutrient management over the immature phase

Rubber trees are the main source of natural rubber (NR). The area occupied by rubber plantations rose from 3.9 million ha in 1961 to 12.5 million ha in 2018. Both the expansion of rubber plantations in marginal zones (prone to biotic and abiotic stress), and long-term rubber tree cultivation in traditional areas, raise questions about the sustainability of NR production in a context of climate change. Our study set out to gain insights into the biogeochemical cycles in rubber plantations, for a better matching of fertilizer inputs to the dynamics of nutrient demand throughout rubber tree growth. Nutrient accumulation in tree biomass is a major component of the biological cycle in tree plantations. We studied the dynamics of biomass and nutrient accumulation in two chronosequences covering the whole lifespan of a plantation in Ivory Coast managed on a sandy soil at the SAPH site, and one on a clayey soil at the SOGB site. In total, 56 trees were destructively sampled in 2-, 5-, 20- and roughly 40-year-old stands. While the use of allometric relationships is common for estimating nutrient stocks in planted forests, this study was the first to provide allometric equations predicting nutrient stocks in rubber tree components. Allometric models were applied to the inventory of 4 commercial stands, for each age at each site, to estimate stand biomass and nutrient stocks. The current annual increments of nutrient stocks in tree biomass peaked between 2 and 5 years after planting. They reached 80 kg ha-1 yr-1 for N, 14 kg ha-1 yr-1 for P and 34 kg ha-1 yr-1 for K at SAPH (53, 7, and 39 kg ha-1 yr-1 respectively at SOGB), which highlighted the importance of an appropriate fertilization schedule for young rubber trees. At the clear-cut age (38–40 years), the amounts of nutrients accumulated in tree biomass were 970 kg N ha-1, 188 kg P ha-1, 366 kg K ha-1, 941 kg Ca ha-1 and 255 kg Mg ha-1 on the sandy soil at SAPH (907,118, 629 1499, and 375 kg ha-1 respectively on the clayey soil at SOGB). Contrasting soil properties and management practices at the two sites had a much greater effect on the amounts of P, K, Ca and Mg accumulated in the trees than on N accumulation. Logging practices in rubber plantations can lead to considerable nutrient exports on poor tropical soils. Harvest residues should be distributed uniformly in the plots so that the roots of young trees can quickly gain access to the nutrients released during decomposition.

Contrasting subsurface denitrification characteristics under temperate pasture lands and its implications for nutrient management in agricultural catchments

Subsurface denitrification plays a key role in the reduction or ‘attenuation’ of nitrate contamination of groundwater and surface waters. We investigated subsurface denitrification characteristics in the vadose zone and shallow groundwater at four sites under pastoral farming in the Manawatū River catchment, located in the lower part of North Island, New Zealand. The denitrification potential of the vadose zone was determined by the laboratory incubation assays measuring the denitrifying enzyme activity (DEA) in soil samples collected from different soil horizons (up to 2.1 m below ground surface), whereas denitrification rates in shallow groundwaters were measured in situ by single-well, push-pull tests conducted in piezometers installed at multiple depths at the study sites. Soils and underlying geology, defining hydrogeologic settings, appear to influence the spatial variability of subsurface denitrification characteristics at the study sites. Where the vadose zone is thin and composed of coarse-textured soils, percolation of nitrate was evident in observed high nitrate-nitrogen concentrations (>5 mg L−1) in oxic and young shallow groundwaters, but low nitrate-nitrogen concentrations (<0.05 mg L−1) were observed in the reduced shallow groundwater found underneath the fine textured soils and/or a thick vadose zone. This was confirmed by the push-pull tests measuring denitrification rates from 0.08 to 1.07 mg N L−1 h−1 in the reduced shallow groundwaters (dissolved oxygen or DO < 0.5 mg L−1), while negligible in the oxic groundwaters (DO > 5 mg L−1) found at the study sites. These contrasting subsurface denitrification characteristics determine the ultimate delivery of nitrate losses from agricultural soils to receiving waters, where the fine textured thick vadose zone and reducing groundwater conditions offer nitrate reduction in the subsurface environment.

Influence of nitrogen supply on macro- and micronutrient accumulation during growth of winter wheat

The understanding of the dynamics of nutrient accumulation in crops is essential to obtain optimal yield and high quality food products. Modern crop production is characterized by high nitrogen (N) rates, which can influence the uptake and concentrations of other nutrients. The aim of this study was to investigate the influence of N fertilization on the temporal accumulation pattern and concentrations of nutrients during the life cycle of a winter wheat crop grown in a cool temperate climate. Seven field trials involving four N treatments (0–240kgNha−1) in southern and central Sweden were sampled over one growing cycle. Above-ground plant parts were sampled at tillering, stem elongation, flowering and full maturity; and the samples were analyzed for macronutrients (N, S, P, K, Ca, and Mg) and micronutrients (Fe, Zn, Mn, Cu, and B). Temporal accumulation pattern of some elements (P, Mg, Zn, Cu, Mn and B) followed biomass accumulation, while other elements (K, Ca, N, S and Fe) accumulated faster than biomass, especially at the early developmental stages and at high N fertilization rates. Low uptake early in the growing season could, at least partly, be compensated by late season uptake with possible implications for nutrient management. In vegetative tissues, the total amounts and concentrations of most macro- and micronutrients (except P, Mn and B) increased with N uptake. In grains, high N rate resulted in increased concentrations of S and Fe, but decreased concentration of K. Enhanced N supply did not generally result in the dilution of other elements in the grain. Results suggest that the high N accumulation rates in high-yielding crops (here winter wheat) are associated with increased demands also of other nutrients, in terms of both increased amounts and tissue concentrations. Nutrient management plans for these crops should accommodate not only the enhanced demand for N, but also other nutrients. Critical threshold concentrations for the avoidance of nutrient deficiencies should be considered in relation to the crop N concentrations.

Denitrification potential in the subsurface environment in the Manawatu River catchment, New Zealand: Indications from oxidation-reduction conditions, hydrogeological factors, and implications for nutrient management

A sound understanding of the effects of hydrogeological factors on loss, transport and transformation of farm nutrients is essential for predicting their impacts on ecosystem health of receiving waters. We assessed the potential of groundwater to attenuate nitrate through denitrification, and the distribution of this potential across the Tararua Groundwater Management Zone (GWMZ) in the Manawatu River catchment, New Zealand. We combined a number of methods in an unprecedented manner to confirm findings and obtain supporting evidence for the features that determine the subsurface denitrification characteristics. Our results showed that the denitrification characteristics of groundwater varied considerably in the Tararua GWMZ. The southern part of the Tararua GWMZ contained mainly oxic groundwater with low potential to denitrify, whereas the middle and northern parts of the Tararua GWMZ contained reduced groundwater with high denitrification potential. The hydrogeological features that influence denitrification potential in groundwater were identified as soil texture and drainage class, and the aquifer material or rock type. Low dissolved oxygen levels and nitrate concentrations were found in groundwater where the combinations of soil and rock types had poor drainage characteristics as opposed to higher concentrations in groundwater under well-drained soils and rocks (e.g. gravels). Intensive pastoral farming over well-drained soils and rocks showed high nitrate concentration in groundwater. This spatial variability in denitrification potential of groundwater offers a targeted management of nutrients runoff and leaching from pastoral lands to reduce their impacts on receiving surface waters.

Nitrogen addition alters carbon and nitrogen dynamics during decay of different quality residues

With the increasing of anthropogenic nitrogen (N) deposition, understanding the underlying mechanisms of external N effect on residue decomposition is critical to improving our prediction of the ecosystem carbon (C) sequestration. An experiment of decay subjected to N addition was conducted by 360 days incubation under laboratory condition, using leaf residues collected from Chinese fir (Cuninghamia lanceolata) (Cl) and eucalyptus (Eucalyptus urophylla) (Eu). Decay of needle leaf (Cl) was slower and more limited by N than broadleaf (Eu). Added N significantly accelerated initial decay, and then the N effect tended to be negative. The switched time point coincided with the C concentration peak, implying C quality might affect the external N impacts. More importantly, our results, together with previous decay studies using multiple residues, illuminated that both the positive and negative N effects became evident as residue quality tended to be low. We supposed that this phenomenon might be attributed to the fact that the specific microbe (fungi, which possessed higher N and C use efficiency than bacteria) gradually exerted a more dominant role in decay with the residue quality varying from high to low, and this shape of microbe would mediate the N impacts. For the isotope signatures, the supplied N caused elevated residue 15N in the early stage, and the increased magnitude was much greater for the hardly-degradable residue (Cl). These 15N dynamics patterns revealed enhanced initial microorganism activity by added N, and also probably confirmed the microbe-mediated effect we presumed. Overall, our research delivered very helpful implications for nutrient management and ecosystem restoration under heightened N scenario in the future.

Nutrient Composition in Litter Fall in Northern Louisiana Hardwood Deciduous Forests

Minor stream bottoms (alluvial floodplains) in the southeastern United States contain large areas of hardwood forests which are a potential sink for upstream nutrients. As a sink, they serve an important role in reducing the loss of nutrients from the sites via the watershed. However, little is known about nutrients stored in forest litter that have the potential to be cycled back to the forest or lost through removal from the site. Three hardwood stands of varying management regimens that span common scenarios found in north Louisiana were sampled for nutrient concentration and quantity in falling litter including leaf, woody, and other debris. Across sites, the well-drained site constitutively contributed more nutrients in litter than the poorly drained sites. Also, the sampling time spanning from March to October had the most litter fall and subsequent nutrient discharge from the trees. Of the five nutrients measured, nitrogen was the largest component followed by potassium. These features in nutrient quantity have broad implications for nutrient management based on site and timing of timber removal. This study provides novel nutrient levels in litter fall of hardwood forests typical along minor stream bottoms.

Strong spatial differentiation of N and P deficiency, primary productivity and community composition between Nyanza Gulf and Lake Victoria (Kenya, East Africa) and the implications for nutrient management

Summary Study of phytoplankton nutrient status, biomass, productivity and species composition was carried out between March 2005 and March 2006, along a transect between north‐eastern open Lake Victoria and the large, shallow Nyanza Gulf in order to examine how the terrestrial run‐off can influence phytoplankton community and nutrient status and determine whether nutrient management of catchment run‐off has the potential to control the algal blooms in the gulf. Hydrological and nutrient differences between the open lake and the gulf create a transition from P deficiency for phytoplankton within the gulf to nitrogen deficiency in open lake. The shallow and turbid gulf was continuously dominated by non‐nitrogen‐fixing filamentous and chroococcale colonial cyanobacteria, but seasonal stratification and deeper mixing depth in the open lake favoured diazotrophic cyanobacteria and diatoms. Seston ratios and metabolic nutrient assays indicated the gulf to be sufficiently phosphorus deficient to impose P limitation on phytoplankton growth and biomass. In contrast, the open lake is not P deficient and is more likely to experience N deficiency that favours diazotrophic cyanobacteria. Because of high turbidity in the gulf, the euphotic zone is very shallow, limiting integral primary productivity compared to the less turbid open lake; high PAR extinction may also favour Microcystis blooms in the gulf. Increased P loading into the gulf may translate to higher algal biomass, mainly of the bloom‐forming and potentially toxic cyanobacteria, and therefore, reduction in P loading into the gulf should be a management priority. However, a review of historical data indicates that the greatest change in water quality in the gulf is increased turbidity that reduces light availability and may limit algal growth more than P deficiency in years of high rainfall and river discharge.

Periphyton response to nitrogen and phosphorus enrichment in a eutrophic shallow aquatic ecosystem

We examined changes in biomass and species dominance of periphyton in response to nitrogen (N) and phosphorus (P) enrichment in 12 mesocosms representing eutrophic aquatic ecosystems. The 100-L mesocosms consisted of lake water and pond sediment, and N and P were applied weekly. Periphyton samples were taken to assess the biomass (as estimated by the concentration of chlorophyll a (chl a)) and to determine which species were dominant. The mean periphyton biomass (chl a) in the P-enriched treatment did not differ from that in the control group, but increased with N enrichment. Compared with that in the control group, the chl a concentration increased with N+P enrichment in the early stages of the experiment, but decreased in the later stages. The decline in periphyton biomass at the later stages of the experiment was due to limited light availability, which resulted from the increased phytoplankton density in the experiment. The nutrient enrichment treatments resulted in changes in the dominant algal species in the periphyton, suggesting that various algal species showed different responses to different nutrients. The results of this study have implications for nutrient management in aquatic ecosystems.

Effects of nitrogen supply and its composition on the growth of Prorocentrum donghaiense

In order to better understand the complex nitrogen (N) dynamics contributing to blooms of the harmful alga, Prorocentrum donghaiense, in eutrophic environments, we compared the growth of this organism on various forms of dissolved inorganic (nitrate and ammonium) and organic N (urea, glutamic acid, peptides and cyanate) compounds both individually and in combination. Growth rates of P. donghaiense were comparable in cultures grown with ammonium, nitrate, urea, glutamic acid, or the dipeptide phenylalanine-alanine as the sole source of N. P. donghaiense could also grow with cyanate or dialanine as sole sources of N, but at lower rates. Different DON urea, glutamic acid or diala:DIN nitrate or ammonium ratios and nitrate:ammonium ratios also affected the growth of P. donghaiense. Growth rates of cultures acclimated on media with combinations of nitrate or ammonium and DON (urea, glutamic acid or alanine-alanine), grew faster than those growing on DON alone. The ratio of nitrate:ammonium in the growth media had little effect on the growth of P. donghaiense. Our uptake experiments exhibited complicated interactions among different nutrients. Nitrate uptake was inhibited by ammonium, glutamic acid and urea. In contrast, ammonium uptake was stimulated by urea and glutamic acid. Further research is needed to understand how the complex mixture of N compounds found in natural systems contributes to the growth and proliferation of P. donghaiense in the environment as this has implications for nutrient management. Because nitrate concentrations are elevated in areas prone to P. donghaiense blooms, nutrient reductions have targeted nitrate. The results presented here suggest that total N loads must be reduced to prevent blooms of this organism in coastal waters.

Modelling nitrogen in the Yeşilirmak River catchment in Northern Turkey: Impacts of future climate and environmental change and implications for nutrient management

Recent research in catchments of rapidly developing countries such as Brazil and China suggests that many catchments of the developing world are already showing signs of nitrogen pollution reminiscent of past experiences in developed countries. This paper looks at both the individual and combined effects of future climate change and other likely environmental changes on in-stream nitrate concentrations in a catchment in Northern Turkey. A model chain comprised of simulated future temperature and precipitation from a Regional Circulation Model (RCM), a conceptual hydrological model (HBV) and a widely tested integrated catchment nitrogen model (INCA-N) is used to model future changes in nitrate concentrations. Two future periods (2021–2050 and 2069–2098) are compared to the 1961–1990 baseline period in order to assess the effectiveness of several possible interventions available to catchment authorities. The simulations show that in the urbanised part of the catchment, the effects of climate change and other environmental changes act in the same direction, leading to peak nitrate concentrations of 7.5 mg N/l for the 2069–2098 period, which corresponds to a doubling of the baseline values. Testing different available policy options reveals that the installation of wastewater treatment works (WWTWs) in all major settlements of the catchment could ensure nitrate levels are kept at near their baseline values for the 2021–2050 period. Nevertheless, a combination of measures including WWTWs, meadow creation, international agreements to reduce atmospheric N concentrations and controls on agricultural practises will be required for 2069–2098. The approach presented in this article could be employed in order to anticipate future pollution problems and to test appropriate solutions, some of which will necessitate international co-operation, in other catchments around the world.

Soil Fertility Variability in Sandy Soils and Implications for Nutrient Management by Smallholder Farmers in Zimbabwe

ABSTRACT In-field variability of soil properties creates niches that have been perceived by smallholder farmers, especially in hostile environments, as constituting an essential part of their subsistence farming. They can exploit niche variability as a risk minimisation strategy for crop production. Smallholder farmers largely base their nutrient management strategies on their perception of niche fertility. The study physically and chemically characterised soil samples up to the 130 cm depth of predominant arable niches from a representative sample of nine smallholder farms with fields cropped for over 70 years. The niches were homestead surroundings, termitaria environments, areas under Parinari curatellifolia and open sandy patches. The data were analysed using discriminant analysis, a statistical method that investigated niche differentiation based on simultaneous analysis of soil nutrient variables. The analysis of variance complemented the discriminant analysis. Results showed that the first two discriminant functions contributed significantly (p < 0.001) to niche differences and accounted for 95% of the total variation. The discrimination was most powerful in classifying termitaria environments and around homestead niches, indicated by greater than 81% aggregation of cases. Termitaria environments had the lowest significant (p < 0.05) bulk density of 1.47 g/cm3 while the remaining niches had bulk densities greater than 1.57 g/cm3. The texture of termitaria environments significantly differed (p < 0.001) from the rest of the niches and consisted of sandy loams and loamy sands. Homestead surroundings, areas under P. curatellifolia and open sandy patches had sandy soils with greater than 90% sand. Macronutrients generally declined with depth. Total C in the 0–20 cm was relatively high in under P. curatellifolia (14.8 Mg/ha) and lowest in the open sandy patches (7.2 Mg/ha). Total N for all niches was low (<1.4 Mg/ha), indicating possible limitation to crop growth. Available P in the active rooting zone of 0–40 cm was adequate only in homestead surroundings (30–50 ppm) and marginal (15–30 ppm) in termitaria environments and under P. curatellifolia. However, it was deficient in the open sandy patches. Homestead surroundings and termitaria environments were the niches with relatively high soil pH (>6.5) and exchangeable base content of Ca, Mg and K. Areas under P. curatellifolia, perceived by farmers to be more fertile, had no comparative advantage over the open sandy patches in texture and macronutrient levels. Farm management practices of applying less nutrient inputs to termitaria environments and areas under P. curatellifolia were misguided and perpetuated low productivity in smallholder cropping environments. We recommend site-specific nutrient management of niches where limited purchased nutrients are applied to relatively fertile niches, for example, homestead surroundings and termitaria environments while open sandy patches are left to recover under natural or improved fallow.

Responses of periphyton to artificial nutrient enrichment in freshwater kettle ponds of Cape Cod National Seashore

Nutrient enrichment bioassays, in conjunction with sampling and analysis of surface water chemistry, were conducted in freshwater lakes (kettle ponds) of Cape Cod National Seashore (Massachusetts, USA) to ascertain the importance of nitrogen (N) and phosphorus (P) in regulating the growth of periphyton. Arrays of nutrient diffusing substrata (NDS) were suspended 0.5 m below the water surface in a total of 12 ponds in July and August 2005. Algal biomass developing on each NDS after ~3 weeks of exposure in each month was assessed by quantifying chlorophyll a + phaeophyton pigments. In both July and August, strong responses to N + P and N enrichments were observed in the majority of ponds, while P had no stimulatory effect. These responses correspond well with low atomic ratios (1–18) of dissolved inorganic nitrogen (DIN) to total phosphorus (TP) in ambient surface waters. The results suggest that conditions in the kettle ponds develop whereby nitrogen is the primary limiting nutrient to periphyton growth. While this may be a seasonal phenomenon, it has implications for nutrient management in individual ponds and within the larger watershed.

The relative contribution of sewage and diffuse phosphorus sources in the River Avon catchment, southern England: Implications for nutrient management

In order to effectively manage nutrient river load reductions and target remediation strategies, it is important to determine the relative contributions of diffuse and point sources across the river catchment. This study used a geographical information system (GIS) to apply phosphorus (P) export coefficients (obtained from the literature) to 58 water quality monitoring sites across a large, urbanised, mixed land use catchment, typical of southern lowland England (the River Avon, Warwickshire, UK). These coefficients were used to estimate the annual P load at each monitoring site, and also the relative contribution of point source (from sewage treatment works (STW)) and diffuse input (from both livestock and agricultural land use). The estimated annual P loads showed very close agreement ( r 2=0.98) with the measured total phosphorus (TP) loads. Sites with the highest proportion of P derived from STW had the highest TP concentrations and loads, and also had greater variations between seasons, with elevated P concentrations occurring during the summer months. The GIS model was re-run to determine the effect of an 80% reduction in P output from STW serving over 10 000 people, thereby assessing the effect of implementing the European Union's Urban Waste Water Treatment Directive (UWWTD). The exported TP load was reduced by 52%, but the sites with the highest TP concentrations were still those with the highest proportion of P derived from STW. The GIS model was re-run to estimate the impact of 80% P reductions at a further 11 STW of varying sizes. This reduced the total TP load by only 29 tonnes year −1, but greatly reduced the P concentrations in many highly nutrient contaminated tributaries. The number of sites with P concentrations greater than 1 mg l −1 was cut from 15 (before UWWTD implementation) to 2. These findings suggest that after UWWTD implementation, resources should focus on introducing tertiary sewage treatment at the remaining large STW, before targeting diffuse inputs. This conclusion is also likely to apply to other lowland river catchments in southern England, most of which have similar population densities to the River Avon.

Approaches and uncertainties in nutrient budgets: implications for nutrient management and environmental policies

Nutrient budgets of agroecosystems are constructed either (i) to increase the understanding of nutrient cycling, (ii) as performance indicator and awareness raiser in nutrient management and environmental policy, or (iii) as regulating policy instrument to enforce a certain nutrient management policy in practice. This paper explores nutrient budgeting approaches and summarizes sources of uncertainty associated with these approaches. Possible implications of uncertainties associated with the different methodologies and approaches for nutrient management and environmental policy are discussed. Three types of nutrient budgets have been distinguished, i.e. farm-gate, soil surface and soil systems budgets. A farm-gate budget is the most integrative measure of environmental pressure, and seems most suitable as environmental performance indicator. A soil surface budget is appropriate for estimating the net loading of the soil with nutrients. Soil system budgets account for nutrient inputs and outputs, recycling of nutrients within the system, nutrient loss pathways and changes in soil nutrient pools; it is the most detailed budget and provides detailed information for nutrient management. Case studies for the dairy farm De Marke indicate that the three budgeting approaches supplement each other. The accuracy and precision of the nutrient budget depend on budgeting approach, data acquisition strategy and type of agroecosystem. There is often a considerable amount of uncertainty in the nutrient budget, due to various possible biases and errors, notably in the partitioning of nutrient losses. Possible sources of biases are personal bias, sampling bias, measurement bias, data manipulation bias and fraud. Sources of errors are sampling and measurement errors. Both biases and errors in nutrient budget estimates may lead to confusion and wrong conclusions. Yet, there is little published evidence that uncertainties are taken into account in decision making. Uncertainties are usually smaller for a farm-gate budget than for a soil surface budget. Therefore, farm-gate budgets are preferred over soil surface budgets as policy instrument. Quantifying uncertainties requires: (a) system identification and analysis, (b) classification of uncertainties, (c) specification of distributions of probabilities of the various sources using Monte Carlo simulation, and (d) monitoring of the nutrient pools, inputs and outputs over time. Analyses of uncertainties in nutrient budgets may provide information about the weakest chain in establishing agri-environmental cause–effect relationships and, therefore, may assist to better focus research efforts. Data for the nitrogen budget of The Netherlands indicate relatively large uncertainties for the items denitrification and leaching, with coefficients of variation >30%. In conclusion, there is a need for standard procedures and guidelines in nutrient budgeting and uncertainty analyses, to improve the confidence in and applicability of nutrient budgets.