Assessing Establishment and Growth of Agricultural Plantings on Reservoir Mudflats

Abstract

Winter drawdowns in flood control reservoirs create expansive mudflats that lack the vegetation typical of littoral zones, which reduces the amount of structure available for fish habitat. This study investigated the feasibility of establishing agricultural plantings as a management action to ameliorate mudflats by providing structural cover following reservoir refilling. We tested cool-season annual grasses and clovers applied in several mixed and monoculture treatments that were sown on the mudflats of Enid Reservoir, Mississippi, during the winter drawdown in three consecutive years. Soil samples were taken for analysis of pH and macronutrients prior to planting. Plantings were monitored until the following spring to evaluate effectiveness of establishment through ground coverage, height, and stem density sampling. Plots were assigned a seeding treatment of either grasses (ryegrass Lolium spp. or triticale x Triticosecale sp.), clovers (balansa clover Trifolium michelianum or berseem clover Trifolium alexandrinum), or both (mixed plantings) or left as an unseeded control. Differences among plant treatments were assessed via repeated measures analysis of variance and differences among means evaluated with Tukey's honestly significant difference test. Soil productivity within the study area was poor all 3 years. Grasses germinated both when disked into the soil and when top sown, while clover only germinated when disked. Plots seeded with grasses performed better than control plots with respect to stem density, height, and ground coverage, while plots seeded with grass and clover mixtures performed better than control plots only with respect to height, and plots seeded with only clover did not perform significantly better than control plots. Results serve as an evaluation of the efficacy of agricultural plant establishment on the mudflats of a flood control reservoir, inform the direction of future research, and identify considerations regarding the application of agricultural plantings as a management tool to create fish habitat.

Selection of Habitat-Enhancing Plants Depends on Predator–Prey Interactions

“…For example, benthic and epiphytic invertebrate communities increase in abundance and species richness with increasing periphyton, detritus, refuge, and living space afforded by submerged vegetation (Cyr and Downing 1988;Schramm and Jirka 1989;Jeffries 1993). Marshall ryegrass outperformed all crops and natural vegetation when planted on reservoir mudflats (Norris et al 2020) and persisted once submerged for up to 3 months (Coppola et al 2019). The results of our study further validate Marshall ryegrass suitability for reservoir mudflat applications.…”

“…These species have diverse architectures, differing in compactness and height. Moreover, they require minimal seedbed preparation for planting, reach maturity prior to submergence from reservoir filling in the spring (Coppola et al 2019), and have been used successfully in reservoir-regulated zones (Norris et al 2020). Thus, the seven plant cultivars along with an unseeded treatment served as our eight plant treatments.…”

“…We used six pots filled with soil from the same source as the plants as an unseeded treatment with no vegetation meant to resemble barren conditions of reservoir mudflats. We used commercial topsoil rather than soils from the regulated zone to standardize substrates and eliminate confounding factors (e.g., highly variable macronutrient and pH levels of reservoir substrates; see Norris et al 2020) that could influence growth.…”

“…In drawdown reservoirs, the culmination of factors that homogenize the lake bottom can limit species diversity (Hatcher et al 2019) and the productivity of fish assemblages by reducing reproductive success (Hassler 1970;Sutela et al 2002;Zohary and Ostrovsky 2011) and juvenile recruitment (Heman et al 1969;Ploskey 1983). The negative consequences of periodic drawdowns on aging reservoirs lead many natural resource managers to habitat enhancement to promote fish communities (Strange et al 1982;Ratcliff et al 2009;Norris et al 2020).…”

“…One option for structural habitat enhancement during drawdowns is sowing shorelines with fast-growing cool season agricultural plants that can reach maturity after drawdown and before flooding (Norris et al 2020). Upon inundation, plantings could provide complex habitat to local biota.…”