Olli Malve

Assessing SWAT model performance in the evaluation of management actions for the implementation of the Water Framework Directive in a Finnish catchment

The ecological status of Lake Pyhajarvi may be classified as moderate due to its elevated nutrient concentrations and algal biomass production. Therefore, the Eurajoki river basin, including Lake Pyhajarvi, has been chosen as the Finnish test catchment in an EU project on benchmarking models for the Water Framework Directive. One aim of the project is to test the suitability of models for the assessment of management options proposed to meet the surface water quality targets. The catchment model SWAT is currently being tested for its applicability for analysing the effectiveness of proposed measures to reduce agricultural and sparse settlement nutrient loading. The model is being applied to the river Ylaneenjoki catchment draining to Lake Pyhajarvi. First results indicate that SWAT can be calibrated for flow and sediment yield using catchment scale parameters. For nutrients, however, parameters describing more detailed catchment processes have to be calibrated. The preliminary essay on measures such as buffer strips indicate that SWAT includes relevant management options that affect nutrient leaching. However, the descriptions of these management options require some modifications in order to describe correctly the reduction efficiency in local conditions.

Internal and external loading as regulators of nutrient concentrations in the agriculturally loaded Lake Pyhäjärvi (southwest Finland)

This study assesses the effects of external and internalloading on the nutrient concentrations in an agriculturallyloaded shallow lake. Using 13 years of observations of thelakes input and outflow, we calculated the long-term balancesof Tot-P and Tot-N. A more detailed balance, which includeddissolved nutrients and suspended solids, was estimated for anice-free period of one year. The contribution of the externalload was assessed using a mass-balance model. The internalload was estimated from the nutrient balances and on the basisof sedimentation measurements and bioassays. The drainagebasin of the lake provided most of the external nutrientinput; the remaining load was derived from atmosphericdeposition to the lake. The proportions of river-transported Pand N in dissolved form were 25% and 77%, respectively. Thelake retained >80% of the external load. Particulatenutrients settled to the bottom and were probably resuspendedseveral times before permanent sedimentation. Dissolvednutrients were bound by primary producers and a highproportion of dissolved P was removed with the fish catch.Dissolved N was also lost via denitrification. Themass-balance model showed that external loading only partlyregulated the mean annual nutrient concentrations in the lake.The regulation was probably due to internal loading, which washigh despite the efficient net retention of nutrients. Duringthe ice-free period, the temporal variations in nutrientconcentrations were controlled almost solely by internalprocesses, such as resuspension of inorganic and organicbottom matter. Although the internal load of bioavailable Pmay, under favourable conditions, exceed the external load,the mechanism by which bioavailable P is translocated from thebottom sediments to the water could not be fully identified.Abbreviations used in this paper follow the editorsrules.

Contamination of river Kymijoki sediments with polychlorinated dibenzo-p-dioxins, dibenzofurans and mercury and their transport to the Gulf of Finland in the Baltic Sea

Kymijoki, the fourth largest river in Finland, has been heavily polluted by pulp mill effluents as well as the chemical industry. Up to 24,000 ton of wood preservative, chlorophenol known as Ky-5, was manufactured in the upper reaches of the river, an unknown amount of which was discharged into the river between 1940 and 1984. Polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs) occurred as impurities in the final Ky-5 product. The PCDD/F concentrations and burden in the river sediments were studied and the transport of PCDD/Fs from contaminated sites downstream and into the Gulf of Finland in the Baltic Sea was estimated. More than 190 sediment cores were sampled to estimate the volume of contaminated sediments and the total PCDD/F burden. The transport of PCDD/Fs was estimated using sediment traps placed at several sites. The survey revealed that sediments in the river were heavily polluted by PCDD/Fs, the main toxic congener being 1,2,3,4,6,7,8-heptachlorodibenzofuran, a major contaminant in the Ky-5 product. The mean total concentration at the most polluted river site downstream from the main source was 42000 microg kg(-1) d.w. (106 microg I-TEQ kg(-1)). The elevated concentrations in the coastal region and the present estimated transport from the River Kymijoki confirm earlier assessments that the river is a major source of PCDD/F for the Gulf of Finland.

Modelling phytoplankton dynamics of the eutrophic Lake Võrtsjärv, Estonia

The aim of the study was to assess the effect of nutrient loading and water level regulation of water quality in Lake Võrtsjärv. The lake is highly eutrophic and it has a high value for fisheries and recreation. A water quality model was developed in order to make predictions of the effects of the different possible restoration measures (reduction of nutrient loading, water level regulation) planned to be carried out. Two phytoplankton groups, diatoms and cyanobacteria, were included in the model. Their contribution to the total algal biomass is dominating. The other state variables of the model are concentration of soluble reactive phosphorus (SRP), concentration of inorganic nitrogen and concentration of dissolved oxygen. The ecological model was constructed using continuously stirred tank reactor (CSTR) hydraulics. The zero-dimensional approach could be used because the lake is shallow and has no thermal stratification. According to the model, external nutrient loading has a very small effect on the biomass of cyanobacteria, whereas the effect is clearer when diatoms are concerned. The contribution of water level to biomass is very significant for both diatoms and cyanobacteria.

Contamination risk of raw drinking water caused by PFOA sources along a river reach in south-western Finland

Transport of perfluorooctanoic acid (PFOA) was simulated in the beginning of River Kokemäenjoki in Finland using one-dimensional SOBEK river model. River Kokemäenjoki is used as a raw water source for an artificial groundwater recharge plant, and the raw water intake plant is located near the downstream end of the model application area. Measured surface water and wastewater concentrations were used to determine the PFOA input to the river and to evaluate the simulation results. The maximum computed PFOA concentrations in the river at the location of the raw water intake plant during the simulation period Dec. 1, 2011-Feb. 16, 2014 were 0.92 ng/l and 3.12 ng/l for two alternative modeling scenarios. These concentration values are 2.3% and 7.8%, respectively, of the 40 ng/l guideline threshold value for drinking water. The current annual median and maximum PFOA loads to the river were calculated to be 3.9 kg/year and 10 kg/year respectively. According to the simulation results, the PFOA load would need to rise to a level of 57 kg/year for the 40 ng/l guideline value to be exceeded in river water at the raw water intake plant during a dry season. It is thus unlikely that PFOA concentration in raw water would reach the guideline value without the appearance of new PFOA sources. The communal wastewater treatment plants in the study area caused on average 11% of the total PFOA load. This raises a concern about the origin of the remaining 89% of the PFOA load and the related risk factors.

Statistical Dimensioning of Nutrient Loading Reduction: LLR Assessment Tool for Lake Managers

Abstract Implementation of the EU Water Framework Directive (WFD) has set a great challenge on river basin management planning. Assessing the water quality of lakes and coastal waters as well as setting the accepted nutrient loading levels requires appropriate decision supporting tools and models. Uncertainty that is inevitably related to the assessment results and rises from several sources calls for more precise quantification and consideration. In this study, we present a modeling tool, called lake load response (LLR), which can be used for statistical dimensioning of the nutrient loading reduction. LLR calculates the reduction that is needed to achieve good ecological status in a lake in terms of total nutrients and chlorophyll a (chl-a) concentration. We show that by combining an empirical nutrient retention model with a hierarchical chl-a model, the national lake monitoring data can be used more efficiently for predictions to a single lake. To estimate the uncertainties, we separate the residual variability and the parameter uncertainty of the modeling results with the probabilistic Bayesian modeling framework. LLR has been developed to answer the urgent need for fast and simple assessment methods, especially when implementing WFD at such an extensive scale as in Finland. With a case study for an eutrophic Finnish lake, we demonstrate how the model can be utilized to set the target loadings and to see how the uncertainties are quantified and how they are accumulating within the modeling chain.

Participatory operations model for cost-efficient monitoring and modeling of river basins — A systematic approach

The worldwide economic downturn and the climate change in the beginning of 21st century have stressed the need for cost efficient and systematic operations model for the monitoring and management of surface waters. However, these processes are still all too fragmented and incapable to respond these challenges. For example in Finland, the estimation of the costs and benefits of planned management measures is insufficient. On this account, we present a new operations model to streamline these processes and to ensure the lucid decision making and the coherent implementation which facilitate the participation of public and all the involved stakeholders. The model was demonstrated in the real world management of a lake. The benefits, pitfalls and development needs were identified. After the demonstration, the operations model was put into operation and has been actively used in several other management projects throughout Finland.

Assimilation of satellite data to 3D hydrodynamic model of Lake Säkylän Pyhäjärvi

To analyze the applicability of direct insertion of total suspended matter (TSM) concentration field based on turbidity derived from satellite data to numerical simulation, dispersion studies of suspended matter in Lake Säkylän Pyhäjärvi (lake area 154 km²; mean depth 5.4 m) were conducted using the 3D COHERENS simulation model. To evaluate the practicality of direct insertion, five cases with different initialization frequencies were conducted: (1) every time, when satellite data were available; (2) every 10 days; (3) 20 days; (4) 30 days; and (5) control run without repeated initialization. To determine the effectiveness of initialization frequency, three methods of comparison were used: simple spatial differences of TSM concentration without biomass in the lake surface layer; averaged spatial differences between initialization data and the forecasts; and time series of TSM concentration and observation data at 1 m depth at the deepest point of the lake. Results showed that direct insertion improves the forecast significantly, even if it is applied less often.

Alternative approaches to modelling lake ecosystems

Abstract The development of modelling in aquatic ecology has focused on mechanistic biogeochemical models. However, such models have substantial data requirements for inputs and also for proper validation, which hinders their use for less studied systems. Another significant problem with complex models is their structural and computational difficulty, and thus often an associated absence of proper uncertainty analysis for the model results. This makes the use of the outputs for public policy making (e.g. in lake management) rather questionable. We see no compelling reason (other than lack of awareness of choices) why all lakes and all questions should necessarily be studied using the same high-profile models. Here we review two alternative statistical approaches, Linear Mixed Modelling and Structural Equation Modelling, and the different ways they have been used to extract maximum information from existing data. These methods offer promise for tackling the problems highlighted above, although our aim is not to promote any one method over the others. Rather, we want to stimulate debate about the remaining unknown factors in lake modelling as well as about the balance between data and models, and the still too uncritical way in which model outputs are interpreted and used for decision making.

Causal analysis of phytoplankton development in a small humic lake using structural equation modelling

Abstract The factors affecting phytoplankton development in a small boreal, dystrophic lake during summer stratification were explored using structural equation models (SEM). Phosphorus had the highest positive impact on phytoplankton, and higher temperatures also enhanced the biomass. Water colour, and to a lesser extent intense zooplankton grazing, restricted phytoplankton biomass. Grazers generally seemed to be ineffective at controlling phytoplankton, however, which could be partly due to the high abundance of Gonyostomum semen (Raphidophyceae), a large motile algae not readily grazed by zooplankton. The importance of water colour, a significant factor in dystrophic lakes, emerged clearer in SEM than from regression models. SEM proved to be an effective and informative technique for exploring the factors affecting phytoplankton development, the role of each variable, and their interactions. Incorporating Bayesian analysis into the traditional SEM enabled a more detailed examination of variation in the variable estimates and possible sources of uncertainty and provided more reliable error estimates. We used total chlorophyll a as a proxy for total phytoplankton biomass, but the results clearly indicated that some of the emerging questions could have been better addressed by separating different phytoplankton groups. Nevertheless, SEM provided new insights from standard data, and we encourage its further applications in aquatic science.