Anne-Mari Ventelä

Long-term time series prediction using OP-ELM

In this paper, an Optimally Pruned Extreme Learning Machine (OP-ELM) is applied to the problem of long-term time series prediction. Three known strategies for the long-term time series prediction i.e. Recursive, Direct and DirRec are considered in combination with OP-ELM and compared with a baseline linear least squares model and Least-Squares Support Vector Machines (LS-SVM). Among these three strategies DirRec is the most time consuming and its usage with nonlinear models like LS-SVM, where several hyperparameters need to be adjusted, leads to relatively heavy computations. It is shown that OP-ELM, being also a nonlinear model, allows reasonable computational time for the DirRec strategy. In all our experiments, except one, OP-ELM with DirRec strategy outperforms the linear model with any strategy. In contrast to the proposed algorithm, LS-SVM behaves unstably without variable selection. It is also shown that there is no superior strategy for OP-ELM: any of three can be the best. In addition, the prediction accuracy of an ensemble of OP-ELM is studied and it is shown that averaging predictions of the ensemble can improve the accuracy (Mean Square Error) dramatically.

Long-Term Field-Scale Experiment on Using Lime Filters in an Agricultural Catchment

The River Yläneenjoki catchment in southwest Finland is an area with a high agricultural nutrient load. We report here on the nutrient removal performance of three on-site lime-sand filters (F1, F2, and F3), established within or on the edge of the buffer zones. The filters contain burnt lime (CaO) or spent lime [CaO, Ca(OH), and CaCO]. Easily soluble lime results in a high pH level (>11) and leads to an efficient precipitation of soluble phosphorus (P) from the runoff. Water samples were taken from the inflow and outflow of each site in different hydrological situations. The length of the monitoring period was 4 yr for F1, 6 yr for F2, and 1.5 yr for F3. F1 and F2 significantly reduced the suspended solids (SS), total P (PTOT), and dissolved reactive P (DRP) in the treated water. The proportional reduction (%) varied but was usually clearly positive. Filter F3 was divided into two equal parts, one containing burnt lime and the other spent lime. Both filter parts removed PTOT and SS efficiently from the water; the burnt-lime part also removed DRP. The mixed-lime part removed DRP for a year, but then the efficiency decreased. The effect of filters on nitrogen compounds varied. We conclude that sand filters incorporating lime can be used together with buffer zones to reduce both P and SS load to watercourses.

Long-term management of Pyhäjärvi (southwest Finland): eutrophication, restoration – recovery?

Abstract Pyhäjärvi, located in the centre of an intensive agricultural area in southwest Finland, is an example of a lake suffering from eutrophication. The lake has been intensively studied for decades and was the object of comprehensive restoration activities both in the catchment and in the lake since the 1990s. During the last 20 years the quality and general usability of water in Pyhäjärvi has deteriorated due to increased algal blooms but has shown some signs of recovery during recent years. These changes have been driven by both a variety of human activities and natural climate related factors such as dry years. Pyhäjärvi has been the object of intensive biomanipulation for decades, carried out by commercial fishermen, whose annual harvest rate approaches the total production of vendace (Coregonus albula), the main planktivore in Pyhäjärvi. The restoration project has also subsidized the harvest of commercially unwanted fish since 1995. In 2002–2006, the EU provided funds for this fishing, which was especially intensive in 2002–2004. The main goal of the future management is to maintain and ensure the current levels of moderately low algal biomass considered acceptable by the financiers and local users of the lake. Achieving the level of water quality during the 1980s is not currently realistic due to current intensive agricultural use of the catchment, lack of cost-effective tools for load reduction from the agriculture, and climate change threats.

What factors control planktonic ciliates during summer in a highly eutrophic lake

A mesocosm experiment in 24 enclosures (6 m3) started at the end of June 1996 in a highly eutrophic shallow lake, Lake Köyliönjärvi (SW Finland). The original factorial design with nutrient, fish and macrophyte treatments was lost due to strong winds causing leakages. However, after the walls were made leak-proof again on July 11, the planktonic communities developed in divergent ways. On July 31 there was a tenfold variation in total crustacean biomass among the enclosures and the lake (40.2–417.5 μg C l−1), and chlorophyll a varied from 9.5 to 67.0 μg l−1. Here, the single-day data on the 25 planktonic communities is analysed by means of correlation and factor analysis in order to identify factors controlling the protozoans, with particular emphasis on ciliates. The data set comprised: total phosphorus, nitrogen, chlorophyll, bacteria, autotrophic picoplankton, heterotrophic flagellates, abundance and species composition of ciliates, phytoplankton and metazooplankton. The results indicate that although the total ciliate abundance (ranging from 16.2 to 95.0 ind l−1) was controlled by food resources, the observed differences in ciliate community structure could be attributed partly to differential predation by metazooplankton. The effect of Daphnia cucullata, the dominant daphnid cladoceran, was stronger than that of other metazoans.

Internal phosphorus load estimation during biomanipulation in a large polymictic and mesotrophic lake

Abstract We quantified internal phosphorus (P) load for 26 years in the polymictic, large (155 km2) and shallow (mean depth 5.5 m) Lake Säkylän Pyhäjärvi, which was heavily biomanipulated by fish removal. Internal load was estimated as (1) partially net estimates from in situ P summer increases, (2) net estimates from P budgets (mass balance approach), and (3) gross estimates from predicted active sediment release area and sediment P release, dependent on August lake temperature. Long-term averages of these estimates were similar and large at about 60% of average external load (105 mg m−2 yr−1) and were larger than external load in years with high water temperature and low water load. Regression analysis revealed that external load is decreasing but internal load is increasing over time. Internal load was negatively correlated with annual water load and positively correlated with lake water temperature. Long-term average annual or summer P concentrations are adequately predicted by a P mass balance model that includes external load, internal load (Method 3), and sedimentation as independently predicted retention. Predictability was poor for individual years, however, partially due to the poor correlation of observed lake and outflow P concentrations, the variable abundance of planktivorous fish, and reflecting the violation of the steady state assumption when individual years are modeled. Scenario modeling shows that biomanipulation cancels out the effects of internal load and forecasts a rapid increase of internal load and P concentration due to climate change; therefore, measures that further decrease external and internal P load and strengthen biomanipulation are recommended.

Perceived environmental quality and place attachment in North American and European temperate lake districts

Abstract Sense of place, or the meanings and attachments held for settings, continues to emerge as an important factor in environmental management. Previous research in a lake-rich setting in northern Wisconsin, USA, demonstrated that attachment to lakes is based in part on the perceived water quality and perceptions of social conflict. This research explores how these findings are similar or different across sites with very different ecological and social characteristics. To explore these cross-site similarities and differences, a social science survey was implemented in 10 lake districts (total n = 2,278 respondents), including 5 sites in North America and 5 in Europe. These sites share several commonalities: they all lie at fairly similar latitudes in the Northern Hemisphere, and they are all regions relatively rich in lake resources. The results demonstrate the myriad commonalities and contrasts in behaviors, environmental perceptions, and place attachment across sites.

Danish and other European experiences in managing shallow lakes

Abstract For a century eutrophication has been the most serious environmental threat to lakes in the densely populated or agricultural areas of Europe. During the last decades, however, major efforts have been used to reduce the external nutrient loading, not least from point sources. Despite these comprehensive efforts, lake eutrophication remains a major problem. Today, the highest pollution input is derived from diffuse sources mainly from agricultural land in lake catchments. We describe the actions taken to reduce the external nutrient loading and the lake responses to these actions as well as the use of additional methods to reinforce recovery, such as biomanipulation. We further discuss resilience and short and long-term responses. We highlight the Danish experiences, but add several examples from restoration measures taken elsewhere in Europe. We also briefly discuss how a potential change in climate may affect lake responses to diminished nutrient loading.

Comprehensive approaches for managing and restoring two large lakes and their catchments: Pyhäjärvi (Finland) and Lake Mendota (USA)

Eutrophication is widely accepted as the most severe threat to i nian d waters. I f nutrient loading i s excessive, algal blooms often develop that can have significant negative effects on the water quality and biodiversity of lakes. The water becomes turbid, toxic blue-green algae may develop, submerged macrophytes disappear, fish communities change into less desirable species and grazing pressure by zooplankton on phytoplankton decreases. The deteriorated water quality threatens municipal and industria! water uses and reduces the recreational va! ue o f the lakes and rivers. Restoration projects have been initiated worldwide to stop this unwanted eutrophication process and to achieve more desirable states of lake ecosystems. In Europe, the Water Framework Directive requires a good ecological status of all surface and ground waters be attained by 2015. In the U. S., laws passed in 1972 and 1977 (Clean Water Act with later amendments) established requirements to restore and maintain the physical, chemical and biological integrity o f the nation s waters. A directive to identify and restore eutrophic lakes is contained in the Act (Clean Lakes, Section 314), which continues to bolster state and local lake restoration efforts. Reaching a good ecological status by lake restoration and management is not an easy task. Complexity of the aquatic ecosystem and anthropogenic activities at both local (e.g. land use changes) and global ( e.g. e li mate change) se a les challenge the success o f water restoration measures. Here we introduce the large-scale lake restoration projects of mesotrophic Pyhiijarvi (southwest Finland) and eutrophic Lake Mendota (Wisconsin, USA). Both projects cover many catchment and in-lake water restoration measures. The results show that even i f nati onal authorities, scientists, municipalities, lake associations and local people would all be willing to support comprehensive restoration and management programs, the recovery process is slow, and the desired result is often not evident. Future challenges for managing the two lakes include changing land use patterns and agricultural policies, altered stream and groundwater hydrologies, introductions of exotic species, and climatic change.

Predation by signal crayfish Pacifastacus leniusculus on fish eggs and its consequences for coregonid recruitment

The character and magnitude of predation by the invasive, ectothermic Pacifastacus leniusculus, a crayfish widely introduced to Europe and Japan from North America, on the eggs of coregonid fishes, vendace Coregonus albula and whitefish Coregonus lavaretus were examined by experimentation, modelling and field data. The present results showed that P. leniusculus has the potential to be very efficient predator of fish eggs under winter conditions, but the predation by P. leniusculus did not significantly decrease production of coregonid larvae during the years with a high P. leniusculus population in the study lake. Hence, the mortality caused by the novel invertebrate predator appeared to compensate for other yet unexplored mortality factors instead of having an additive effect on the present salmonids.

Responses of Aquatic Ecosystems to Environmental Changes in Finland and China

The concern for the state of global freshwater reservoirs has increased due to deterioration of the water quality during the last decades. This has prompted monitoring and restoration efforts such as the European Water Framework Directive and the national-scale 2nd-investigation and monitoring of the water quality, water volume and biota resources in China. The challenge so far has been the determination of the “natural” state (reference conditions) of freshwater ecosystems. We used the sediment archives of five lakes and one brackish water embayment in Finland and China to assess the impact of selected variables of climatology, hydrology, nutrients, and changes in human population on these ecosystems during the last few centuries. The study sites represent catchment areas with varying land use. Despite the long distance between the sites and their different land-use characteristics, the direction and timing of changes during the last few centuries are well comparable between the high latitudes of Finland and the mid-low latitudes of China. This study reinforces the sensitivity of aquatic ecosystems to environmental change and underlines the usefulness of the palaeolimnological approach as a tool for determining reference conditions.