Effects of successional stage and plant association on moist soil unit macroinvertebrates.

Abstract

Aquatic macroinvertebrates are an important food resource for waterfowl wintering and staging in seasonally flooded impoundments. Therefore, it is important to manage these areas for maximum production of this food resource. The abundance of aquatic macroinvertebrates in seasonally flooded moist soil units is commonly linked to the type of vegetation present, with early successional stage plants typically having higher numbers of species and greater biomass relative to later successional stages. Little work has been done in Kansas wetlands to ascertain which successional stages produce the highest amount of aquatic macroinvertebrates, so management practices can be employed to ensure an optimal yield of this resource. Additionally, little work has been done to determine which plants are associated with the highest production of aquatic macroinvertebrates and what time of the year aquatic macroinvertebrates are in high enough numbers to be an important food resource in east-central Kansas. To determine what time of year, what age and what plant associations have the highest number, greatest biomass and highest diversity of aquatic macroinvertebrates I sampled 0, 1, 2, 3 and 20 year old moist soil units on the Flint Hills National wildlife Refuge (FHNWR) in Lyon and Coffey counties, Kansas and on adjacent private land (McKinney Marsh) in Coffey County, Kansas. After sampling vegetation, I selected the top ten plant association types occurring within these moist soil units and used them to test for differences in invertebrate biomass, number, and diversity among different plant groupings. I captured aquatic macroinvertebrates through the use of activity traps and a core sampler in 8 separate moist soil units during the period of 29 September 1992 to 30 April 1993. I collected macroinvertebrates from a total of 60 activity traps and 60 core samples for each unit. I found 28 families within 9 orders of aquatic macroinvertebrates during my study. Significant differences were found among the trap and core sample means for both moist soil unit and plant association type invertebrate mean biomass, mean number, and diversity by month, with the exception of moist soil unit trap diversity by month. In most cases biomass, number and diversity were higher in the fall than the winter and spring, suggesting that invertebrates are potentially more important as a food resource to waterfowl staging on the FHNWR rather than overwintering waterfowl. Although I expected earlier successional stages to have higher amounts of invertebrates, no significant differences were found among the trap and core samples for moist soil unit invertebrate mean biomass, mean number, and diversity by successional stage, with the exception of moist soil unit mean core biomass by successional stage. I attribute this lack of significance to the flooding that covered my study sites with up to 5 m of water during parts of November through March and prevented access for several weeks at a time. The flooding washed away a majority, and in some cases all, of the standing vegetation and detritus on my study sites. Similarly, I found no significant differences among the trap and core samples for plant association type invertebrate mean biomass, number, and diversity, with the exception of core diversity. Again I attribute this lack of significance to the flooding. Although my study is inconclusive relative to the relationship between aquatic macroinvertebrate presence and moist soil unit successional stage and plant association, it has provided a starting point, some baseline data for future research on the FHNWR, and may indicate the importance of flooding as a disturbance to aquatic macroinvertebrate communities in moist soil units.