EFFECTS OF WATER FLOW ON A WETLAND MACROINVERTEBRATE COMMUNITY

Macroinvertebrates make up a large fraction of secondary production in wetlands
and are strongly influenced by hydrologic alterations. However, little is known of the
effect flow has on macroinvertebrate production and community composition in wetlands.
Reintroducing measurable water velocities (1-5 cm/s) to the oligotrophic (phosphoruslimited)
Everglades has the potential to affect macroinvertebrate production and
community structure by increasing the supply of phosphorus (P) to periphyton, changing
basal food quality, and physically altering the habitat. In Chapter 2, I investigated the
potential effects of flow-mediated nutrient-loading on the growth rate of herbivorous
grazers, apple snails (Pomacea maculata), by growing periphyton on standard substrates,
in four sloughs within a landscape-scale flow addition experiment; two sloughs received
elevated flow velocities (2.9-5.2 cm/s) and two control sloughs (0.3-0.4 cm/s). Snails fed
periphyton from the flowing sloughs gained more than 3.7-fold greater total mass than
snails fed periphyton from the control sloughs. The highest velocity slough produced the
greatest snail growth. Snail growth was correlated with P accumulation and C:P ratios in
the periphyton. Water column nutrients were low and the water column TP differences among sloughs could not fully explain differences in periphyton nutrients or snail growth.
Increasing flow above background conditions by as little as 2.4 cm/s in this oligotrophic
wetland altered periphyton food quality by flow loading, which subsequently increased
growth rates of primary consumers. In Chapter 3, I investigated potential changes in
macroinvertebrate standing stock biomass and community composition caused by flow by
conducting two sweep net surveys. Surveys were conducted within two groups of sloughs,
flow sloughs (6 sloughs) and control sloughs (12 sloughs), within the same landscape-scale
flow addition experiment as the growth experiment. Surveys were conducted from January
to March in 2018 and 2021. Biomass was compared between the flow sloughs and control
sloughs using generalized linear models. Community composition was analyzed at the
slough level using Bray-Curtis similarity. Biomass of macroinvertebrates was similar
among transects in 2018 but higher in the flow sloughs in 2021 with the highest biomasses
further from the L67A (velocities <2cm/s). The two highest flowing sloughs (typically
>3cm/s) had a different community composition from the other 16 sloughs in both 2018
and 2021 with a predator resistant non-native snail appearing in 2021. The results of the
surveys show an increase in macroinvertebrate production in the flow sloughs possibly
related to increased nutritional value of food, however, with higher biomass further from
the L67A and the invasion of a predator resistant snail at the high flow sloughs, it also
appears that there is increased top-down pressure on the macroinvertebrates at the sloughs
closer to the L67A (were cover from predation has been reduced). The overall results of
these studies indicate flow produces more nutritional food for herbivorous
macroinvertebrates and increases standing stock biomass but can change the community
composition when periphyton cover is reduced.