A large proportion of nutrients and sediment is mobilised in catchments during storm events. Therefore understanding a catchment's hydrological behaviour during storms and how this acts to mobilise and transport nutrients and sediment to nearby watercourses is extremely important for effective catchment management. The expansion of available in-situ sensors is allowing a wider range of water quality parameters to be monitored and at higher temporal resolution, meaning that the investigation of hydrochemical behaviours during storms is increasingly feasible. Studying the relationship between discharge and water quality parameters in storm events can provide a valuable research tool to infer the likely source areas and flow pathways contributing to nutrient and sediment transport. Therefore, this paper uses 2 years of high temporal resolution (15/30 min) discharge and water quality (nitrate-N, total phosphorus (TP) and turbidity) data to examine hysteretic behaviour during storm events in two contrasting catchments, in the Hampshire Avon catchment, UK. This paper provides one of the first examples of a study which comprehensively examines storm behaviours for up to 76 storm events and three water quality parameters. It also examines the observational uncertainties using a non-parametric approach. A range of metrics was used, such as loop direction, loop area and a hysteresis index (HI) to characterise and quantify the storm behaviour. With two years of high resolution information it was possible to see how transport mechanisms varied between parameters and through time. This study has also clearly shown the different transport regimes operating between a groundwater dominated chalk catchment versus a surface-water dominated clay catchment. This information, set within an uncertainty framework, means that confidence can be derived that the patterns and relationships thus identified are statistically robust. These insights can thus be used to provide information regarding transport processes and biogeochemical processing within river catchments.

Analysis of hydrochemical behaviour during storm events can provide new insights into the process controls on nutrient transport in catchments. The examination of storm behaviours using hysteresis analysis has increased in recent years, partly due to the increased availability of high temporal resolution data sets for discharge and water quality parameters. A number of these analyses involve the use of an index to describe the characteristics of a hysteresis loop in order to compare storm behaviours both within and between catchments. This technical note reviews the methods for calculation of the hysteresis index (HI) and explores a new more effective methodology. Each method is systematically tested and the impact of the chosen calculation on the results is examined. Recommendations are made regarding the most effective method of calculating a HI which can be used for comparing data between storms and between different water quality parameters and catchments.

Plastic mulch films support global food security, however, their composition and the potential release rates of organic, metal and metalloid co-contaminants remains relatively unknown. This study evaluates the low molecular weight organic additives, metal and metalloid content and leaching from low density polyethylene (LDPE) and biodegradable plastic mulch films. We identified 59 organic additives, and non-intentionally added substances in the new LDPE films (39.8 mg m^-2) and 60 in the new biodegradable films (129 mg m^-2). The leaching of organic compounds of high concern for ecosystem and human health (e.g. phthalates, organophosphite antioxidants) was comparable to those of low concern (fatty acids, fatty amides, alkanols). However, the majority of leached compounds have undergone no regulatory scrutiny and their environmental fate and toxicity remain unknown. Leaching of heavy metals (Cu, Zn, Pb) was low relative to inert fillers (Ca, Na). Leaching was higher for both organic and metal/metalloid additives from the biodegradable films (74.6 mg m^-2) than the LDPE films (23.7 mg m^-2). This untargeted approach allowed assessment of the chemical burden posed to individual farms, based on existing use patterns of plastic mulch films, with higher chemical burden coming from biodegradable films, raising the potential for pollution swapping. This research emphasises the need to include the complex mixture of leached additives when assessing the environmental risks presented by plastic mulch films, balancing yield benefits with the protection of our agricultural soils.

Diffuse water pollution from agriculture (DWPA) is a major environmental concern, with significant adverse impacts on both human and ecosystem health. However, without an appropriate understanding of the multiple factors impacting on water, mitigation measures cannot be targeted. Therefore, this paper addresses this gap in understanding, reporting the hydrochemical monitoring evidence collected from the UK Government's Demonstration Test Catchments (DTC) programme including contrasting chalk and clay/mudstone catchments. We use data collected at daily and sub-daily frequency over multiple sites to address: (1) How does the behaviour of the full range of nitrogen (N) species and phosphorus (P) fractions vary? (2) How do N species and P fractions vary inter- and intra-annually? (3) What do these data indicate about the primary pollution sources? And (4) which diffuse pollution mitigation measures are appropriate in our study landscapes? Key differences in the rates of flux of nutrients were identified, dependent on catchment characteristics. Full N speciation and P fractionation, together with dissolved organic carbon (DOC) enabled identification of the most likely contributing sources in each catchment. Nitrate (NO3-N) was the dominant N fraction in the chalk whereas organic and particulate N comprised the majority of the load in the clay/mudstone catchments. Despite current legislation, orthophosphate (PO4-P) was not found to be the dominant form of P in any of the catchments monitored. The chalk sub-catchments had the largest proportion of inorganic/dissolved organic P (DOP), accompanied by episodic delivery of particulate P (PP). Contrastingly, the clay/mudstone sub-catchments loads were dominated by PP and DOP. Thus, our results show that by monitoring both the inorganic and organic fractions a more complete picture of catchment nutrient fluxes can be determined, and sources of pollution pin-pointed. Ultimately, policy and management to bring nutrient impacts under control will only be successful if a multi-stressor approach is adopted.