Effects of woody debris, microtopography, and organic matter amendments on the biotic community of constructed depressional wetlands

To increase wetland acreage and biodiversity, Delaware agencies constructed >220 depressional wetlands. During construction, agencies included amendments thought to increase biodiversity. Because the efficacy of amendments is unknown, we investigated their effects on macroinvertebrate and vegetative communities. We selected 20 standardized wetlands (five contained coarse woody debris (CWD) and microtopography amendments (land surface ridges and furrows), five had neither, five had CWD only, and five had microtopography only). Additionally, 12 wetlands had received organic matter amendments (i.e., straw). Insect richness (P = 0.010; r2 = 0.16), insect biomass (P = 0.023; r2 = 0.13), intolerant insect biomass (P = 0.033, r2 = 0.03), Ephemeroptera biomass (P = 0.027; r2 = 0.12), and Odonata biomass (P = 0.046; r2 = 0.10) increased with CWD volume. Obligate plant percent cover increased with microtopographic variation (P = 0.029; r2 = 0.120). Although organic matter amendments did not increase percent soil organic matter (t13.7 = −1.16, P = 0.264), total (P = 0.027; r2 = 0.12), native (P = 0.036; r2 = 0.11), and facultative (P = 0.001; r2 = 0.24) plant richness increased with percent soil organic matter. To enhance biodiversity, constructed wetlands should contain CWD, but additional research is needed to understand the benefits of microtopography and organic matter amendments.