Seppo Rekolainen

Diversity predicts stability and resource use efficiency in natural phytoplankton communities.

The relationship between species diversity and ecosystem functioning has been debated for decades, especially in relation to the “macroscopic” realm (higher plants and metazoans). Although there is emerging consensus that diversity enhances productivity and stability in communities of higher organisms; however, we still do not know whether these relationships apply also for communities of unicellular organisms, such as phytoplankton, which contribute ≈50% to the global primary production. We show here that phytoplankton resource use, and thus carbon fixation, is directly linked to the diversity of phytoplankton communities. Datasets from freshwater and brackish habitats show that diversity is the best predictor for resource use efficiency of phytoplankton communities across considerable environmental gradients. Furthermore, we show that the diversity requirement for stable ecosystem functioning scales with the nutrient level (total phosphorus), as evidenced by the opposing effects of diversity (negative) and resource level (positive) on the variability of both resource use and community composition. Our analyses of large-scale observational data are consistent with experimental and model studies demonstrating causal effects of microbial diversity on functional properties at the system level. Our findings point at potential linkages between eutrophication and pollution-mediated loss of phytoplankton diversity. Factors reducing phytoplankton diversity may have direct detrimental effects on the amount and predictability of aquatic primary production.

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 andnitrogen losses and concentrations in Finland during the period1981–1997 were studied in 15 small agricultural and forestedcatchments. In addition, four coastal river basins with highagricultural land use located in southern Finland were includedin the study in order to assess the representativeness ofagricultural loss estimates from small agricultural catchments.The mean annual loss specific for agricultural land was estimatedto be on average 110 kg km-2 a-1 for total phosphorusand 1500 kg km-2 a-1 for total nitrogen. The resultsfrom small agricultural catchments were in agreement with thecorresponding loss estimates from rivers, with an average of137 kg km-2 a-1 for total phosphorus and 1800 kg km-2a-1 for total nitrogen. The results from the studiedagricultural catchments and rivers during the period 1981–1997suggest that weather-driven fluctuation in discharge was usuallythe main reason for changes in nutrient losses, and little or noimpact of changes in agricultural production or managementpractises can be observed. In forested areas the total phosphorusloss (average 9 kg km-2 a-1) and total nitrogen loss(average 250 kg km-2 a-1) were lower than inagricultural areas. In forested catchments the impact of forestryoperations, such as clear-cutting and fertilization, and theimpact of atmospheric nitrogen deposition can be seen in changesin nutrient losses.

Loss of plant species richness and habitat connectivity in grasslands associated with agricultural change in Finland.

Abstract The drastic loss of seminatural grasslands and the decrease in species diversity in Europe during the 20th century are closely linked to social-economic factors. Development in agricultural production drives land-use changes, and thus controls the capacity of landscapes to maintain biodiversity. In this study, we link agricultural production changes to landscape fragmentation and species diversity. Our results show that the termination of grazing on seminatural grassland caused significant changes in landscape structure and a decline in the number of vascular plant species. The decline of grazed grasslands has been driven mainly by farm-level economic efficiency and profitability interests, which have been connected with agricultural policy measures. Since 1995, when Finland joined the European Union, the area of grazed patches in our study area has again increased as a result of a support scheme for the management of seminatural grasslands.

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.

A conceptual framework for identifying the need and role of models in the implementation of the water framework directive

Abstract The new European Water Framework Directive (WFD) aims at improving water quality using an integrated approach to implement necessary societal and technical measures. Successful implementation of the WFD requires appropriate mathematical models and other tools to manage different phases of the planning procedure and to support decision making in various steps of the implementation process. Design, development, testing and use of these tools call for the development of a conceptual framework, which provides a basis to assure that proper tools will be available and selected for defined purposes. We developed the well‐known DPSIR framework to fit better to the WFD implementation process, and to this framework we identified which types of models are needed in different consecutive steps of the process. The framework, which we call the DPCER framework and which links to different model types, (i) is dynamic, (ii) indicates cause‐consequence relationships, (iii) integrates human and natural science, and (iv) is policy relevant. Its purpose is to bring the potential model applications into a wider perspective and lay a foundations for the selection of models and other tools within the identified three different phases of WFD implementation.

Evaluation of the accuracy and precision of annual phosphorus load estimates from two agricultural basins in Finland

Abstract The accuracy and precision of phosphorus load estimates from two agricultural drainage basins in western Finland were evaluated, based on continuous flow measurements and frequent flow-proportional sampling of total phosphorus concentration during a 2 year period. The objective was to compare different load calculation methods and to evaluate alternative sampling strategies. An hourly data set of concentrations was constructed by linear interpolation, and these data were used in Monte Carlo runs for producing replicate data sets for calculating the accuracy and precision of load estimates. All estimates were compared with reference values computed from the complete hourly data sets. The load calculation methods based on summing the products of regularly sampled flows and concentrations produced the best precision, whereas the best accuracy was achieved using methods based on multiplying annual flow by flow-weighted annual mean concentration. When comparing different sampling strategies, concentrating sampling in high runoff periods (spring and autumn) was found to give better accuracy and precision than strategies based on regular interval sampling throughout the year. However, the best result was obtained by taking samples flow-proportionally within the highest peak flows plus additional regular interval (e.g. biweekly) samples outside these flow peaks. Using this strategy, which calls for automatic sampling equipment, accuracies better than 5% and precisions better than 10% can be achieved with only 30–50 samples year−1.

Ecological threshold responses in European lakes and their applicability for the Water Framework Directive (WFD) implementation: synthesis of lakes results from the REBECCA project

The objective of this synthesis is to present the key messages and draw the main conclusions from the work on lakes in the REBECCA project, pointing out their links to theoretical ecology and their applicability for the WFD implementation. Type-specific results were obtained from analyses of large pan-European datasets for phytoplankton, macrophytes, macroinvertebrates and fish, and indicators and relationships showing the impact of eutrophication or acidification on these biological elements were constructed. The thresholds identified in many of the response curves are well suited for setting ecological status class boundaries and can be applied in the intercalibration of classification systems. Good indicators for phytoplankton (chrysophytes, cyanobacteria) and macrophytes (isoetids and charaphytes) responses to eutrophication were identified, and the level of eutrophication pressure needed to reach the thresholds for these indicators was quantified. Several existing metrics developed for macrophytes had low comparability and need further harmonisation to be useful for intercalibration of classification systems. For macroinvertebrates, a number of metrics developed for rivers turned out to be less useful to describe lake responses to eutrophication and acidification, whereas other species based indicators were more promising. All the biological elements showed different responses in different lake types according to alkalinity and humic substances, and also partly according to depth. Better harmonisation of monitoring methods is needed to achieve better precision in the dose–response curves. Future research should include impacts of hydromorphological pressures and climate change, as well as predictions of timelags involved in responses to reduction of pressures.

Phosphorus reference concentrations in European lakes

As part of an assessment of the ecological quality of surface waters, recent European water legislation, the water framework directive (WFD), requires the setting of environmental objectives for particular chemicals. As part of this, many European countries are choosing to develop a quality classification scheme for total phosphorus (TP) concentration. The assessment of ecological quality and its component parts, such as TP, must be based on the degree of divergence of a water body from an appropriate baseline, or ‘reference condition’. For this reason, it is important to determine TP reference conditions for all lake types, or alternatively, models for predicting reference TP concentrations on a site-specific basis. With this purpose in mind, we have assembled a large dataset of European lakes considered to be in reference condition; 567 lakes in total. Data has been collated on TP concentration, mean depth, alkalinity, humic type, altitude, area, and geographical region. Reference TP concentrations have been derived from this dataset using two empirical approaches. Firstly, lake-type specific TP reference conditions were derived simply from descriptive statistics (median and percentiles) of TP concentrations by lake type. Secondly, empirical models were developed for estimating site-specific reference TP concentrations from a set of potential predictor variables. TP concentrations were found to vary with lake type and by geographical region. TP increased with colour and alkalinity, and decreased with lake depth and altitude. There was no clear relationship between TP and lake area. Altitude, mean depth and alkalinity were selected as independent explanatory variables for prediction of site-specific reference TP concentrations, with different models developed for humic and non-humic lakes. A simpler site-specific predictive model based solely on the morphoedaphic index (MEI) (a combination of a site’s alkalinity and mean depth) was also shown to be comparably effective.

MODELING SEDIMENT YIELD AND PHOSPHORUS TRANSPORT IN FINNISH CLAYEY SOILS

A mathematical simulation model (ICECREAM), describing the phosphorus cycle in the soil and its losses from soil to water, was developed and applied to clayey soils in Finland. The model is based on the CREAMS and GLEAMS model, with some modifications to adapt it to local (climatic) conditions. The original erosion submodel (USLE) highly overestimated erosion for Finnish agricultural clayey soils with relatively steep slopes (i.e., 7%–8%). The calibration of poorly known and/or spatially varying input parameters, such as Manning’s n, soil erodibility, and field capacity, did not sufficiently improve the agreement between simulated and measured data. Therefore, a sensitivity analysis of the erosion equations was carried out using Monte Carlo methods, varying both input and non–input parameters. This analysis showed that parameters in equations dependent on the slope, such as rill and interrill detachment rates, peak runoff rate, and equations related to sediment transport capacity were the most sensitive. Thus, those parameters were recalibrated, resulting in simulated annual sediment yields that approached the measured erosion rates, which ranged from 200 to 5000 kg ha –1 yr –1 . Since the amount of phosphorus bound to sediments is closely correlated with the amount of eroded soil material, simulated sediment–bound phosphorus also corresponded better to the measurements.

Estimation of the impact of fertilisation rate on nitrate leaching in Finland using a mathematical simulation model

Agriculture comprises the largest single source of nitrogen (N) into watercourses in Finland. The emphasis of water protection policy is today on controlling the non-point nutrient losses from agriculture. In this study a mathematical simulation model was used as a management tool to estimate the changes in nitrate (NO3 -N) leaching resulting from changes in cultivation practices in Finnish agriculture caused by the Agri-Environmental Support Scheme as a part of the Common Agricultural Policy of the European Union. Detailed data were collected from about 400 farms by interviewing farmers in four study areas in different parts of the country. The potential impacts of these changes on nitrate losses were then assessed by a deterministic nitrogen leaching model and regional assessments were made by combining the results of model calculations with digital spatial data about soils, crops and fertilisation, using GIS-software. In general, the use of nitrogen fertilisers (inorganic fertilisers and manure) has decreased to meet the requirements of the Support Scheme. However, the estimated potential impacts on nitrate losses were rather small (3‐14% in different study areas). The model results showed that to achieve the targeted national and international reductions in agricultural nitrate leaching, fertilisation and particularly manure spreading should be reduced and adjusted better to the actual nitrogen requirements of crops.