A practical approach to improve the statistical performance of surface water monitoring networks.

The representativeness of aquatic ecosystem monitoring and the precision of the assessment results are of high importance when implementing the EU's Water Framework Directive that aims to secure a good status of waterbodies in Europe. However, adapting monitoring designs to answer the objectives and allocating the sampling resources effectively are seldom practiced. Here, we present a practical solution how the sampling effort could be re-allocated without decreasing the precision and confidence of status class assignment. For demonstrating this, we used a large data set of 272 intensively monitored Finnish lake, coastal, and river waterbodies utilizing an existing framework for quantifying the uncertainties in the status class estimation. We estimated the temporal and spatial variance components, as well as the effect of sampling allocation to the precision and confidence of chlorophyll-a and total phosphorus. Our results suggest that almost 70% of the lake and coastal waterbodies, and 27% of the river waterbodies, were classified without sufficient confidence in these variables. On the other hand, many of the waterbodies produced unnecessary precise metric means. Thus, reallocation of sampling effort is needed. Our results show that, even though the studied variables are among the most monitored status metrics, the unexplained variation is still high. Combining multiple data sets and using fixed covariates would improve the modeling performance. Our study highlights that ongoing monitoring programs should be evaluated more systematically, and the information from the statistical uncertainty analysis should be brought concretely to the decision-making process.

Lakes in the Finnish Eurowaternet: status and trends.

The Eurowaternet is a monitoring network designed to cover all European countries, with the overall objective of obtaining timely, quantitative and comparative information on the status of inland waters so that their key environmental problems can be defined, quantified and monitored. Finland launched the Eurowaternet for lakes in 2000. The network was set up according to guidelines of the European Environment Agency (EEA) and was based on national, regional and local monitoring programmes. It includes 253 lake sites, divided into the following groups by, for example, their loading background and size: (i) reference sites, (ii) point-source loading (impact) sites, (iii) agricultural sites, (iv) representative sites, i.e. lakes <100 km(2) with typical water quality in the catchment and (v) lake deep sites in large lakes (>100 km(2)). We examined the water quality and its development during 1976-2001 in these groups, using data from surface and near-bottom water layers at summer and winter stagnation. In addition, the representativeness of the network was evaluated. Summer mean concentrations of total P (TP) during 1990-2001 in surface water were (i) 6.8+/-1.8 microg 1(-1) in reference lakes, (ii) 24+/-5 microg 1(-1) in lakes affected by point loading, (iii) 58+/-32 microg l(-1) in agricultural lakes, (iv) 14+/-2.2 microg l(-1) in representative lakes and (v) 11+/-2.1 microg l(-1) in large lakes. Comparison with reference lakes revealed major impact of human activities on TP and total N (TN)-and consequently on chlorophyll a (a-chl) and transparency-in all other groups, especially agricultural lakes. Decreasing TP and increasing O(2) trends were found at impact sites, reflecting water protection measures taken in pulp and paper mills and municipalities. More surprisingly, we found increasing alkalinity trends in all but agricultural sites and decreasing NO(2)-N+NO(3)-N (NO(x)-N) trends particularly in pelagic areas of large lakes. Comparison of water quality in Eurowaternet lakes with those in randomly sampled lakes (Finnish Lake Survey) revealed that the Eurowaternet covers the entire range of concentrations of TP, TN and conductivity in Finnish lakes, but <1-km(2), eutrophic and/or brown water lakes are underrepresented. Only 0.2% of a total of 13114 small lakes (0.1-1 km(2)) are included in the annual monitoring program of the Eurowaternet.