Drainage ditching at the catchment scale affects water quality and macrophyte occurrence in Swedish lakes

Summary 1. We have limited knowledge of the effects of land use in general and of drainage ditching in particular on macrophyte communities in lakes. I quantified catchment land use, including drainage ditching, as well as water quality and the number of macrophyte species in 17 Swedish lakes in summer 2005. 2. Land use within 1 km of the studied lakes was analysed in a geographic information system. The following variables were included: areas of forests, mires, agricultural land and urbanization, length of drainage ditches (classified according to the use of the land they drained), and shortest distance from lake to an urban area. To extract and analyse general trends in the data sets, redundancy analysis was used. 3. Water quality was explained mainly by three land-use related variables: the lengths of agricultural, forest and mire ditches. The length of agricultural ditches was positively correlated with lake water conductivity, total dissolved solids, Ca, N and total organic carbon (TOC). The lengths of forest and mire ditches were positively correlated with lake water characteristics, especially TOC. 4. The number of species representing different macrophyte life forms was explained by three environmental variables: conductivity, and lengths of forest and agricultural ditches. The numbers of isoetids, nymphaeids, elodeids and total obligate hydrophytes were negatively correlated with length of forest ditches. In contrast, the number of lemnids and helophytes was positively correlated with conductivity and length of agricultural ditches. Furthermore, the number of isoetids was exponentially related (negatively) to lengths of agricultural and forest ditches, indicating a threshold response to drainage ditch length. 5. The results suggest that effects on water quality and macrophyte communities result from drainage ditching in the lake catchments rather than from land use itself. Given the total area of drainage-ditched land worldwide (millions of ha in Scandinavia alone), drainage ditching should be considered when evaluating environmental impacts on lake water quality and macrophyte occurrence and when determining reference conditions for catchment land use.

[1]  S. Jensen.  Classification of lakes in Southern Sweden on the basis of their macrophyte composition by means of multivariate methods , 1979, Vegetatio.

[2]  J. Holden,et al.  Artificial drainage of peatlands: hydrological and hydrochemical process and wetland restoration , 2004 .

[3]  P. Chow-Fraser,et al.  Primary determinants of macrophyte community structure in 62 marshes across the Great Lakes basin: latitude, land use, and water quality effects , 2001 .

[4]  M. Åström,et al.  Impact of Ditching in a Small Forested Catchment on Concentrations of Suspended Material, Organic Carbon, Hydrogen Ions and Metals in Stream Water , 2001 .

[5]  Spring bryophytes in forested landscapes: Land use effects on bryophyte species richness, community structure and persistence , 2005 .

[6]  H. Toivonen,et al.  Aquatic macrophytes and ecological gradients in 57 small lakes in southern Finland , 1995 .

[7]  R. P. Pandey,et al.  Groundwater recharge by channel infiltration in El Barbon basin, Baja California, Mexico , 1999 .

[8]  N. Willby,et al.  Using aquatic macrophyte community indices to define the ecological status of European lakes , 2008, Aquatic Ecology.

[9]  P. Manninen.  Effects of forestry ditch cleaning and supplementary ditching on water quality , 1998 .

[10]  S. Dodson,et al.  LAND USE, WATER CHEMISTRY, AQUATIC VEGETATION, AND ZOOPLANKTON COMMUNITY STRUCTURE OF SHALLOW LAKES , 2005 .

[11]  M. Åström,et al.  Effect of ditching operations on stream-water chemistry in a boreal forested catchment. , 2001, The Science of the total environment.

[12]  T. Rintanen.  Changes in the flora and vegetation of 113 Finnish lakes during 40 years , 2001 .

[13]  M. Palmer,et al.  A botanical classification of standing waters in Britain: Applications for conservation and monitoring , 1992 .

[14]  P. Belleau,et al.  Effects of drainage of a forested peatland on water quality and quantity , 1999 .

[15]  P. Dale,et al.  Managing Salt Marshes for Mosquito Control: Impacts of Runnelling, Open Marsh Water Management and Grid-ditching in Sub-tropical Australia , 2006, Wetlands Ecology and Management.

[16]  E. Jutila,et al.  Influence of environmental factors on the density and biomass of stocked brown trout, Salmo trutta L., parr in brooks affected by intensive forestry , 1999 .

[17]  K. Vuori,et al.  Impact of forest drainage on the macroinvertebrates of a small boreal headwater stream : Do buffer zones protect lotic biodiversity ? , 1996 .

[18]  O. Pietiläinen,et al.  Chlorophyll reference conditions for European lake types used for intercalibration of ecological status , 2008, Aquatic Ecology.

[19]  J. Downing,et al.  The influence of watershed land use on lake N: P in a predominantly agricultural landscape , 2001 .

[20]  E. Jutila,et al.  Instream and catchment characteristics affecting the occurrence and population density of brown trout, Salmo trutta L., in forest brooks of a boreal river basin , 2001 .

[21]  Michael J. Vanni,et al.  Phytoplankton primary production and photosynthetic parameters in reservoirs along a gradient of watershed land use , 2003 .

[22]  E. Jutila,et al.  Forest drainage: a threat to benthic biodiversity of boreal headwater streams? , 1998 .