Lake Pyhäjärvi /River Ylaneenjoki (Finland)

REFRESH Catchment case studies - responding to future change: Lake Pyhäjärvi /River Ylaneenjoki (Finland)

Pyhäjärvi lake location mapLake Pyhäjärvi is the largest lake in south‐western Finland. It is shallow and mesotrophic and is important for commercial fishing. Eutrophication, mostly due to agriculture, been a major concern since the late 1980s as cyanobacteria blooms have become more and more frequent. 

Response of the lake to changing climate and land use

The ecological response of Lake Pyhäjärvi to future climate and land use changes has been assessed by combining scenarios of future change with chained watershed, river and lake models. Total phosphorus (TP) and chlorophyll a (Chl-a) concentrations were simulated to detect if changes in air temperature and precipitation predicted as a result of climate change will enhance the algal growth in lakes. The effects of management measures to decrease the algae concentrations are also simulated.

For a range of climate change scenarios, models predicted increases in both Chl‐a and TP which would result in a change in WFD classification status from Good to Moderate. Four land‐use scenarios were modelled, from intensive agriculture to environmental ‘green’ scenarios. Intensive agriculture scenarios changed the status of the lake from Good to Moderate, while under 'green' scenarios it remained in Good status.

Pyhäjärvi lake monitoring station(Left) The real‐time lake monitoring station was set up on 22 May 2010 in Lake at the Finnish demonstration site. Photo: Pia Mattila‐Lonka

The land‐use change scenarios seem to have a more pronounced impact on the lake than climate change scenarios although the former do incorporate some elements of the latter, and it is possible that land‐use changes are needed to ‘catalyze’ climate change impacts. The interactions and feedback mechanisms between these changes are highly complex, however, with numerous changes in hydrological dynamics, snow/frost conditions in milder winters, catchment and lake processes, cultivation practices and timings, crop types etc.

Management measures, best and worst scenarios

Following modelling runs incorporating management measures we found that increases in winter vegetation (e.g. 40% coverage) appeared to decrease Chl‐a concentration while reductions in P fertilization did not have a clear impact. The probability of achieving Good status is higher if P is the target variable. The effectiveness of measures (e.g. 40% increase in winter vegetation) was tested with climate change scenarios – worst and best cases, with and without measures. Based on the model runs the increase in winter vegetation measure seems as effective under future climate change and, indeed, may be more effective.

The cost-effectiveness analysis of water protection measures in agriculture was assessed, together with possible additional benefits from improved water quality. We studied costs, effects and benefits in two different time horizons: until 2015 and until 2027. The lake is presently in Good status, but very close to the threshold between Good and Moderate and is Moderate half the time, when problems with eutrophication occur. The measures are implemented by farmers and thus it is here that the costs of protection are borne. However, the farmers are compensated for undertaking mitigation measures, which makes the state and the tax payers the actual cost-bearer.

The cost-effectiveness of several combinations of mitigation measures to increase winter time vegetation coverage were considered;

  1. Increasing the amount of winter cereals
  2. Changing from cultivator tillage to direct sowing
  3. Increasing the amount of nature management fields

The analysis showed that there are cost-effective combinations of these measures which reduce nutrient load and at the same time, may even reduce the costs of farming. A benefit transfer method was used to quantify the potential benefits that can be gained from reaching the set protection target.

The study shows that the lake’s Good status is precarious and increased water protection measures are needed to ensure it doesn't shift to Moderate. The analysis of potential benefits suggests that considerable benefits can be gained from meeting the protection goal. There is thus a social need to continue protection of the lake. Comparison of costs of protection and potential benefits to be gained indicates that benefits are clearly higher than the costs.

For further information see the below REFRESH reports

Workshop proceedings on collaborative scoping of solutions, Lake Pyhäjärvi/River Yläneenjoki catchment, Finland

Cost-effectiveness Analysis reports for the Lake Pyhäjärvi/River Yläneenjoki catchment, including analysis of proportionality/disproportionality

Pyhäjärvi/Yläneenjoki modelling: final report

Synthesis of work at Lake Pyhäjärvi/River Yläneenjoki catchment