Short-term effects of soil amendments in restoring riparian habitat following gravel mining in an urban inland lake

Background/Question/Methods Budgetary constraints prevent municipalities from restoring degraded habitats, popular restoration techniques (e.g., control burns) may not be permitted in urban locations, and others (e.g., planting native species) may be prohibitively expensive or labor-intensive.  Riparian habitats are vulnerable to anthropogenic degradation, despite their ecological importance, afterwards exhibiting impoverished soils and simplified plant communities dominated by invasive, exotic species.  We investigated the effects of soil amendments on riparian vegetation of an urban lake in Michigan.  Altered by extensive gravel mining, the lake is adjacent to the city’s Clean Water Plant, a railway, interstate highway, and several industrial plants.  We employed a randomized, complete block design of 1 m² plots among two slope positions (upper vs. lower slope) to study the effects of manure (added once) and sawdust mulch + sucrose (added annually).  Prior to applying soil amendments 2005, we collected soil samples and surveyed vegetation in plots to determine baseline values of soil nutrients, plant diversity and species abundance, repeating these procedures in 2006 and 2007.  We calculated community diversity using Simpson’s Indices, comparing treatment effects using negative natural log values (ANOVA; 2005 data = covariate).  Changes in soil nutrient concentrations and species abundance were analyzed by PERMANOVA (2005 data = covariate).  

Results/Conclusions Slope position affected organic matter (higher in upper-slope plots) and abundance Aster vimineus (small white aster; higher in lower-slope plots).  Sawdust + sucrose amendments reduced nitrate-N levels and, coupled with slope position, suppressed the rate of expansion of Centaurea maculosa (spotted knapweed).  Manure increased soil phosphorus and organic matter and fostered the persistence of Festuca rubra (red fescue) and Plantago lanceolata (English plantain).  Thus, despite the brief duration of this study, these simple soil amendments significantly affected soil nutrients and several key plant species (including an invasive of great concern in the region).  We expect the treatments to have more conspicuous effects in future years as succession continues and the changes in soil nutrients are sustained over time.