Trends of phosphorus, nitrogen and chlorophyll a concentrations in Finnish rivers and lakes in 1975-2000.

During recent decades the amounts of nutrients discharged to Finnish surface waters have markedly decreased. This has been achieved by considerable investments in water protection, which were made mainly to improve municipal and industrial wastewater purification. We investigated whether these water protection measures have decreased phosphorus and nitrogen concentrations in Finnish rivers and lakes. In addition, possible trends in chlorophyll a concentrations in lakes were studied. The data consisted of a total of over 68000 monitoring results of 22 rivers and 173 lakes (or sub-basins of lakes) with different types of catchment areas. The study period covered the years 1975-2000 and the non-parametric Kendall Tau b and Seasonal Kendall tests were applied for detecting trends. Decreasing nutrient concentration trends were typical in many lakes and rivers earlier polluted by municipal and industrial wastewaters. Increasing nutrient concentration trends were common in smaller rivers and lakes receiving diffuse loading from agriculture. The results show that the investments directed towards wastewater purification have effectively improved the quality of Finnish inland waters. However, no clear effects of decreasing non-point loading were found. Thus, more effective measures should be directed towards decreasing non-point source loading.

Losses of nitrogen and phosphorus from agricultural and forest areas in Finland during the 1980s and 1990s.

The temporal changes and spatial variability of phosphorus and nitrogen losses and concentrations in Finland during the period 1981-1997 were studied in 15 small agricultural and forested catchments. In addition, four coastal river basins with high agricultural land use located in southern Finland were included in the study in order to assess the representativeness of agricultural loss estimates from small agricultural catchments. The mean annual loss specific for agricultural land was estimated to be on average 110 kg km(-2) a(-1) for total phosphorus and 1500 kg km(-2) a(-1) for total nitrogen. The results from small agricultural catchments were in agreement with the corresponding loss estimates from rivers, with an average of 137 kg km(-2) a(-1) for total phosphorus and 1800 kg km(-2) a(-1) for total nitrogen. The results from the studied agricultural catchments and rivers during the period 1981-1997 suggest that weather-driven fluctuation in discharge was usually the main reason for changes in nutrient losses, and little or no impact of changes in agricultural production or management practises can be observed. In forested areas the total phosphorus loss (average 9 kg km(-2) a(-1)) and total nitrogen loss (average 250 kg km(-2) a(-1)) were lower than in agricultural areas. In forested catchments the impact of forestry operations, such as clear-cutting and fertilization, and the impact of atmospheric nitrogen deposition can be seen in changes in nutrient losses.

Managing radioactively contaminated land: implications for habitat diversity.

Radioactive contamination of agricultural land may necessitate long-term changes in food production systems, through application of selected countermeasures, in order to reduce the accumulation of radionuclides in food. We quantified the impact of selected countermeasures on habitat diversity, using the hypothetical case of two agricultural areas in Finland. The management scenarios studied were conversions from grassland to cereal production and from grassland and crop production to afforestation. The two study sites differed with respect to present agricultural production: one being predominantly cereal production and seminatural grasslands, while the other was dominated by intensive grass and dairy production. Some of the management scenarios are expected to affect landscape structures and habitat diversity. These potential changes were assessed using a spatial pattern analysis program in connection with geographic information systems. The studied landscape changes resulted in a more monotonous landscape structure compared to the present management, by increasing the mean habitat patch size, reducing the total habitat edge length and reducing the overall habitat diversity calculated by the Shannon diversity index. The degree of change was dependent on the present agricultural management practice in the case study sites. Where dairy production was predominant, the landscape structure changes were mostly due to conversion of intensive pastures and grasslands to cereal production. In the area dominated by cereal production and seminatural grasslands, the greatest predicted impacts resulted from afforestation of meadows and pastures. The studied management changes are predicted to reduce biodiversity at the species level as well as diminishing species-rich habitats. This study has predicted prominent side effects in habitat diversity resulting from application of management scenarios. These potential long-term impacts should be considered by decision-makers when planning future strategies in the event of radionuclide deposition.

Modeling combined effects of forestry, agriculture and deposition on nitrogen export in a northern river basin in Finland.

The development of the spatial N export and retention model N_EXRET for large river basins is presented, utilizing remote-sensing-based land use and forest classification. Export coefficients describing the contribution from agriculture, forestry and peat harvesting were estimated based on empirical studies. Representativeness of forest treatment coefficients have been evaluated by use of data from a small, well-documented test catchment. Simulation results from the application of the model to the Oulujoki river basin (22,840 km2) are discussed. Model estimated N fluxes were compared with measured N fluxes in separate points of the river basin. Based on source apportionment, agriculture contributes 17% of the total export, varying between 8% in the uppermost subbasin and 38% in the lowermost subbasin close to the sea. Forestry contributes almost as much, 16%, with less pronounced variation (11-24%) between the different subbasins. In the separate subbasins, 7-37% of the incoming gross N export was retained. Based on mass balances and sensitivity analyses, retention was estimated to be in the range of 5-10 kg ha-1 yr-1 in lakes and 0-1 kg ha-1 yr-1 in peatlands. The model results were validated by testing to data from the 3 closely situated river basins. However, further testing is needed in river basins where land use and deposition patterns differ clearly from these northern basins.