Many lakes and rivers are badly affected by algal blooms, which are often caused by phosphorus pollution. This study compares different ways of estimating phosphorus inputs to our waterways and highlights the large amount of uncertainty generated by different methods of sampling and data interpretation. In general, high frequency monitoring is needed to implement and manage nutrient reduction programs effectively.

Reference conditions exhibit natural concentrations of chemical indicators of water quality and therefore can be used to determine the anthropogenic input. Using data from > 1000 water quality sites, a method was developed to estimate median concentrations of chemical indicators under reference conditions for New Zealand streams and rivers and account for natural variation in climate, hydrology and geology as classified by the River Environment Classification (REC). By incorporating natural variation, reference conditions can then be used to help inform water quality objectives and avoid setting water quality limits or targets that are either too restrictive, and impossible to meet (e.g. below reference conditions), or too high, such that they have little ecological benefit.

Inputs of nitrogen, phosphorus, sediment and faecal matter from dairy farming are a major cause of degraded water quality. Results from a monitoring study of five dairy catchments and their streams showed that increased fencing of streams to keep cattle out, and greater use of effluent irrigation of markedly improved water quality. Monitoring periods of at least 10 years are necessary to detect such changes.

High levels of nutrients have caused algal blooms in Lough Leane, Ireland, an important tourist location. Investigations of nutrient sources found that although agriculture provided more nutrients annually, the local Wastewater Treatment Plant played a crucial role in phosphorus loading during summer, when river discharge was low. Managers need to take account of such seasonal differences when targeting causes of blooms.

US agriculture is vitally important to world food supplies, but needs to improve environmental performance under a changing climate while intensifying production. This review highlights healthy functioning soil as being critical to ensure U.S. agriculture's resilience under these converging pressures. Reversing soil degradation will accrue wide benefits for agriculture and for the quality of freshwater and marine resources.

Enhanced nutrient loading by farming activity often causes eutrophication in shallow lakes in lowland areas but can also affect water quality in large and deep lakes. In Lake Brunner, a large and deep nutrient poor lake, nutrient concentrations and algal biomass have increased since 1992. These observations are likely to have resulted from enhancement of pasture drainage and effluent inputs from expanding dairy farms.

Managing dairy runoff in high rainfall areas is challenging. In this study, we characterise loads and concentrations in a small dairy catchment stream entering an oligotrophic lake and identify mitigation opportunities. Key loss pathways were drainage to groundwater and surface runoff in storms, and best management practices included reducing losses of fertiliser P, better management of dairy farm effluent and managing stock during winter (wintering).

Sustainable development is enhanced by tools that predict effects on a wide range of economic, social and environmental values. We developed a computerised ‘knowledge network’ to predict the likely states of key values in response to development scenarios involving irrigation-driven intensification of farming, on-farm pollution control measures, and dam location. The approach has assisted catchment management planning locally and has wider potential use.

In China, rapid development in population and economy has led to environmental degradation to an extent that currently jeopardises the quality of water resources. We linked a complex watershed-model with an empirical water quality model for a Chinese drinking water reservoir. Results suggest that point sources and diffuse pollution are equally important in the degradation of surface water quality, and display how a series of management interventions may improve water quality.