Manipulating the hydroperiod affects plant and invertebrate communities in freshwater mesocosms, La Marque TX USA, 2019-2021

We used a mesocosm experiment with six flooding depths and seven drought durations, followed by seven months of recovery, to explore how freshwater wetlands typical of the Houston, Texas area would respond to different hydrological regimes that might occur if wetlands were drained in anticipation of a heavy rain that did not materialize, leading to a temporary period of little or no standing water. The experiment was conducted in 2019-2021. How quickly mesocosms dried out was a function of initial water depth, with mesocosms initially set with greater water depths (30 cm) taking on average 38 days to dry out. Individual plant species (14 were planted; 8 were common at the end of the recovery period) were affected drought length, flooding depth, or their interaction, with results varying among species. The composition of the plant community at the end of the drought period was strongly affected by drought length, and this effect persisted through seven months of recovery, with the 80- and 160-day drought treatments diverging most strongly from shorter drought treatments. Densities of mosquito larvae, snails and tadpoles were temporally variable, and affected more during the treatment period than after seven months of recovery. Our results indicate that managed wetlands in southeast Texas would be quite resilient to dry periods of up to 40 days in duration, especially if water was not completely drained at the beginning of the drought. In addition, some wetland species would persist in managed wetlands even if they experienced droughts of up to 160 days.

本研究采用中宇宙实验（mesocosm）设置6种淹水深度与7种干旱时长梯度，并设置7个月的恢复期，旨在探究德克萨斯州休斯顿地区典型淡水湿地，在湿地为防范未发生的暴雨而提前排水、进而出现短暂近乎无积水状态的不同水文情势下的响应规律。本实验于2019至2021年间开展。中宇宙的干涸速率取决于初始水深：初始设置水深为30 cm的中宇宙平均耗时38天方可完全干涸。供试植物共14种（恢复期结束后仍有8种为常见物种），其生长与存活分别受干旱时长、淹水深度或二者交互作用的影响，且不同物种的响应模式存在显著差异。干旱期结束时的植物群落组成显著受干旱时长影响，且该影响在7个月的恢复期内持续存在：其中80天与160天干旱处理组的群落组成与短时长干旱处理组的差异最为显著。蚊幼虫、螺类与蝌蚪的种群密度随时间动态变化，且在实验处理阶段受到的影响显著大于7个月恢复期后。本研究结果表明，德克萨斯州东南部的人工管理湿地对最长40天的干旱期具有较强的恢复力，尤其在干旱初期未完全排干水体的情况下。此外，即便遭遇长达160天的干旱，部分湿地物种仍可在人工管理湿地中存续。