Table 1.
Physical and chemical characteristics of surveyed ditches.
Table 2.
Connectivity, land use and management of ditches.
Participation in agri-environment schemes (AES) includes Entry Level Stewardship Schemes (ELS), Higher Level Stewardship Schemes (HLS) and Environmentally Sensitive Areas (ESA) (http://www.naturalengland.org.uk/ourwork/farming/funding/default.aspx)
Table 3.
Results from final model in partial redundancy analyses of community data using the final model selected, using forward stepwise selection with double stopping criteria (Blanchet et al 2008).
Significance of each term in the final model was tested using 999 permutation tests: a type I test (in sequential order) and type III test (test of marginal significance).
Table 4.
Amount of variation explained by environmental (Env) and conditioned (Site and Quadrat Size) variables in the partial redundancy analyses of the bank vegetation community, channel vegetation community and aquatic invertebrate community (see Table 3 for environmental factors included in final models, conditioned variables were always site and quadrat).
Conditioned variables are treated as covariates and held constant whilst investigating the amount of variation accounted for by explanatory variables. Some variation is explained jointly by environmental and conditioned data sets (cannot be attributed to either data set) as they are not orthogonal [55].
Fig 1.
Correlation biplots from the final partial RDA models showing species and explanatory variables for a) bank vegetation b) channel vegetation and c) aquatic invertebrates.
In a) shade was entered as a quadratic term. Species codes consist of [first 3 letters of genus name]_ [first 3 letters of species name], see S1 Dataset for full taxonomic names.
Fig 2.
Species richness of aquatic plants per 10 m length of ditch bank plotted against percentage shade over ditch channel.
Regression line fitted from a simple linear model of predictor plotted against response without random effects.
Table 5.
Model selection table from analyses with response variables i) Channel vegetation species richness; ii) Invertebrate taxonomic richness and iii) Number of Ephemeroptera, Plecoptera and Trichoptera (EPT) families per ditch.
Only models which were a better fit than the null model are listed.
Fig 3.
Invertebrate sample taxonomic richness in relation to a) average water depth b) percent shade over the ditch channel and c) mean taxonomic richness in relation to percent arable land in the surrounding fields.
Regression lines are fitted from a linear model of predictor plotted against response without random effects.
Fig 4.
Number of Ephemeroptera, Plecoptera and Trichoptera (EPT) families per ditch in relation to a) pH and b) temporal connectivity of ditch and time since dredged (black circles and line, permanent ditches, open triangles and dashed line temporary ditches).
Error bars (c) are 95% confidence intervals. Regression lines are fitted from a generalised linear model with poisson distribution of predictor plotted against response without random effects.
Table 6.
Management of ditches in agri-environment schemes (AES) in England (Entry Level Stewardship, Higher Level Stewardship, Environmentally Sensitive Areas, Countryside Stewardship Scheme [38]) and those not in AES.
Data in square brackets beneath are ditches from sites where land managers had both ditches that were managed under AES and those managed outside of AES.