The Effects of Soil Properties of Formerly Embanked Saltmarshes on Vegetation Growth and Diversity

Abstract

The threat of sea level rise causes many countries to spend time and money on coastal protection. One such protective measure is the de-embankment of former saltmarshes, in order to restore them to functional ecosystems with creeks and vegetation. However, during the time of embankment, these areas were often under agricultural management that turned the land into crop-fields or pastures. The difference in land-use might have had lasting effects on the soil, which could in turn affect the vegetation growth and diversity. This paper contains an overview of observed and possible ways in which the soil properties of formerly embanked saltmarshes affect vegetation growth and diversity. Soil compaction caused by heavy tillage machinery or cattle trampling cannot only make it harder for roots and shoots to penetrate the soil, but it also negatively affects creek formation and drainage of the marsh, which is detrimental to vegetation diversity. This is exacerbated by a low topographic heterogeneity that hinders creek formation. Original research shows that the heterogeneity usually does not increase over time but instead seems to deteriorate. In addition, soil compaction leads to a low marsh surface elevation, which further impedes biodiversity. Excessive fertilizer use before de-embankment might also influence vegetation growth and diversity, as it can lead to high nutrient environments which could favor certain species and induce algal proliferation. Lastly, it may cause the soil of higher elevations to become more acidic. The severity of these factors is likely different pertaining to zonation on the marsh: where the lower marsh elevations likely deal more with factors relating to drainage, higher elevations could be more affected by penetration resistance, high nutrient concentrations and acidification.