IWRA Proceedings

AbstractWater quality management requires scientifically sound data as a base for the decision making process. This data should be provided by suitable monitoring systems. In Chile, like in other countries, information requirements with regard to water quality are determined by the national water policy and legislation. In addition, monitoring system design needs to take into consideration the variability of the natural processes as well as pressures exerted to the systems by human activities, including pollution sources, water abstractions and climate change. At the end, social and political aspects determine how important water quality monitoring is for the country or region and economic factors will determine which monitoring intensity is feasible. However, a sound scientific knowledge can help to allocate resources for monitoring in the most efficient way. The objectives of the presented contribution are to scrutinize recent water quality legislation in Chile regarding information demands and to analyse spatial and temporal variability of key water quality constituents in five river basins in North-Central Chile for the 26-33 ºS realm (Aconcagua, Ligua, Huasco, Limari, Choapa) based on existing water quality related data through GIS and statistical analysis. This analysis lays down the basis for suggestions on an improved monitoring system in these watersheds. The water quality legislation is analysed according to the stipulated quantitative information requirements regarding water quality constituents. These requirements belong to the fields of impact, compliance, and trend monitoring, each type having different demands according to the statistical design. The five watersheds, which differ in size, climate, land use, and development status, are analysed according to their topography, surface water networks, water flows, point and diffuse sources of pollution, and land use. The spatio-temporal analysis on a watershed basis illustrates that in some cases spatial correlation allows the exclusion of several existing monitoring sites, whereas in other cases the high temporal variability of parameters asks for higher measuring frequency than the actual (four times a year) in order to satisfy statistical needs and to support an effective decision-making process. To provide an example the case of nitrate in the Aconcagua watershed is elaborated in more detail. Modelling results show that spatio-temporal variability asks for a redesign in terms of monitoring site location and frequency, supporting an optimized allocation of financial means to satisfy the requirements of the secondary water quality norm. At the same time the study reveals the existing knowledge gaps regarding the behaviour of constituents within the watershed systems, which inhibits an improved monitoring design. Subsequently, concrete suggestions for a future research programme are elaborated in order to fill the data gaps. In particular it seems necessary to study the behaviour of pollutants like heavy metals and nutrients at a sub-watershed level. Finally, some qualitative statements are presented regarding a possible impact of climate change on water quality issues. Here, special reference is made to the design of trend monitoring networks in the watersheds under scrutiny.