Insect Community Diversity Tracks Degradation and Recovery of a Wastewater Assimilation Marsh in Southeast Louisiana
Total Page：16
File Type：pdf, Size：1020Kb
Insect Community Diversity Tracks Degradation and Recovery of a Wastewater Assimilation Marsh in Southeast Louisiana M. O. Weller & J. L. Bossart Wetlands Official Scholarly Journal of the Society of Wetland Scientists ISSN 0277-5212 Volume 37 Number 4 Wetlands (2017) 37:661-673 DOI 10.1007/s13157-017-0897-1 1 23 Your article is protected by copyright and all rights are held exclusively by Society of Wetland Scientists. This e-offprint is for personal use only and shall not be self- archived in electronic repositories. If you wish to self-archive your article, please use the accepted manuscript version for posting on your own website. You may further deposit the accepted manuscript version in any repository, provided it is only made publicly available 12 months after official publication or later and provided acknowledgement is given to the original source of publication and a link is inserted to the published article on Springer's website. The link must be accompanied by the following text: "The final publication is available at link.springer.com”. 1 23 Author's personal copy Wetlands (2017) 37:661–673 DOI 10.1007/s13157-017-0897-1 ORIGINAL RESEARCH Insect Community Diversity Tracks Degradation and Recovery of a Wastewater Assimilation Marsh in Southeast Louisiana M. O. Weller1 & J. L. Bossart1 Received: 24 June 2016 /Accepted: 2 March 2017 /Published online: 20 March 2017 # Society of Wetland Scientists 2017 Abstract The assimilation of wastewater effluent into wet- Introduction lands is used to combat land loss in Southeast Louisiana. This study reports on changes in benthic insect diversity at a Human caused habitat loss, in the form of land transformation wetland assimilation site over the course of multiple years of or habitat destruction, is widely understood to be the leading sampling, during which time an initially healthy marsh de- cause of biodiversity loss (Vitousek 1994; Pimm and Raven graded to open water and subsequently partially-revegetated. 2000;WWF2016). The wetlands of the Mississippi Delta are Insects are commonly used to monitor the health of streams a habitat of particular concern, as multiple factors are contrib- and rivers, but have rarely been used to study wetlands. Three uting to their rapid degradation and disappearance (e.g. log- year-long sampling bouts resulted in a collection of 3984 in- ging, oil exploration and extraction, introduction of invasive dividuals, representing 33 families and 86 species. Insect di- species, hydrological isolation, and rising sea levels) (Day versity tracked the overall condition of the marsh over time. et al. 2007;Lopez2009; Shaffer et al. 2009). Between 1932 Simpson’s diversity was highest before degradation occurred, and 2010, Louisiana lost an estimated 1883 mi2 of wetlands, lowest at the height of degradation, and intermediate during equaling a quarter of the total wetland area present in 1932. the period of partial recovery. Species richness, however, was This loss is continuing at an estimated rate of ~16 mi2/year, highest in the partially revegetated marsh community. which is the highest rate globally, and accounts for 90% of Although this community included species characteristic of coastal land loss in the United States (Britsch and Dunbar both the intact and degraded communities, it shared greatest 1993;Barrasetal.2003; Barras 2006; Couvillion et al. 2011). affinity with the intact marsh. The dominant taxa present in To understand the extent of damages and degradation to these communities shifted from various beetles to chironomid any ecological system, and the efficacy of any restoration flies and then back to beetles. Our finding that insect families efforts, reliable indicators are needed that reveal the relative readily track wetland condition will be a valuable manage- condition, or integrity, of these habitats, from intact to degrad- ment tool given the dramatically decreased time and expertise ed. Ecological integrity is an emergent property of a mosaic of needed to identify specimens to family versus species. multiple factors, such as community composition and diversi- ty, the functioning and efficiency of certain ecological pro- cesses, and the suite of abiotic and biotic environmental con- Keywords Louisiana . Freshwater wetland degradation . ditions that facilitate these communities and processes (Karr Wastewater assimilation . Insect community diversity 1991; Dale and Beyeler 2001). Because an overwhelming amount of information is present for any environment, collect- ed data must be sifted through in order to identify key surro- * M. O. Weller gates, or ecological indicators, that can reveal the condition of [email protected] the whole system (Karr 1981; Dale and Beyeler 2001;Niemi and McDonald 2004). In wetland systems, water quality met- rics, such as pH, dissolved oxygen, salinity and temperature, 1 Department of Biological Sciences, Southeastern Louisiana University, SLU 10736, 2400 N. Oak Street, Hammond, LA 70402, have often been used to quantify and track habitat condition. USA However, as these physical data are not themselves a part of Author's personal copy 662 Wetlands (2017) 37:661–673 the living system, their value as indicators is limited. Sampling family, Chironomidae, is still an indicator of habitat degrada- components of the living system, such as plant, microbial, or tion, occurring at higher abundances with increasing coverage insect communities, provides a biological snapshot that better of open water. captures effects of multiple stressors over time (Barbour et al. Tertiary treatment of wastewater via wetlands assimilation 1999). has been advanced as a mechanism for increasing the integrity Insects possess multiple qualities that make them ideal eco- of natural or degraded wetlands, and is known to be an energy logical indicators. They are hyperdiverse, accounting for more and cost effective alternative to traditional water treatment than 80% of the Earth’s total species (Wilson 1992); fill a wide methods (Breaux et al. 1995;Koetal.2004; Kadlec and range of functional roles in ecosystems, including pollination, Wallace 2009). There is a large body of research outlining pest control, prey for vertebrates, decomposition, and nutrient the positive effects of this type of treatment, including multi- cycling; often have large population sizes; and have relatively ple success stories of assimilation projects, both regionally quick life cycles and thus respond rapidly to environmental (Day et al. 2004;Hunteretal.2009) and globally (Kadlec changes (Mattson and Addy 1975; Madden and Fox 1997; and Wallace 2009; Vymazal 2010), including examples spe- Schowalter et al. 1998; Bossart and Carlton 2002). In many cific to tropical ecosystems (Tanaka et al. 2011), and less cases the relative diversity of insect communities has been developed nations (Kivaisi 2001). Wastewater assimilation directly tied to that of plant and vertebrate communities and has the potential benefit of reintroducing nitrogen and phos- to the condition of the overall ecosystem (Cox et al. 1998, phorous, essentially mimicking nutrient inputs from seasonal Shokri et al. 2009). Insect communities in healthy habitats river flooding that contribute to the natural creation of deltas are often characterized by higher diversity, containing a wide and still sustain wetlands outside of levee boundaries (Reddy variety of families within many orders, relative to these same et al. 1993; Rybczyk et al. 2002; Day et al. 2004). Freshwater habitats when they are degraded (Helgen 2002; Weigel and input, whether by wastewater assimilation or river diversions, Dimick 2011). Habitat condition may also be indicated by the also helps buffer wetlands from saltwater intrusion (McKee presence or absence of specific taxa. For example, in rivers et al. 2004; Martin and Shaffer 2005;Laneetal.2007). and streams, dominance by chironomid flies is associated with degraded or polluted habitats, whereas a significant presence of the orders Ephemeroptera, Plecoptera and Tricoptera indi- Objectives and Predictions cates intact habitats (Weigel and Dimick 2011). Insects are abundant in aquatic habitats and have long been The primary objective of this study is to quantify changes that used to assess the relative condition of streams and rivers occurred in the insect assemblage at Four Mile Marsh, a nat- (Wallace and Webster 1996). While similar studies of wetland ural marsh in the Lake Pontchartrain Basin that was targeted habitats are less common, these have been steadily increasing for tertiary processing of secondarily treated wastewater. in number (Batzer and Wissinger 1996). Wetlands in temper- Initially, we had hypothesized that insect diversity would in- ate regions of North America have received the most attention crease in concert with the influx of the nutrient rich discharge and these constitute a variety of wetland types, including nat- of water into the marsh as a consequence of increased vege- ural and constructed marsh (Murkin et al. 1992; Chow-Fraser tative quality. Instead, the discharge of wastewater resulted in et al. 1998; Galbrand et al. 2007;Drinkardetal.2011; Culler an unexpected nearly complete shift in vegetative cover, et al. 2014), seasonal woodland ponds (Batzer et al. 2004; transforming the marsh from an intact, fully vegetated habitat, Brooks 2000), and peatlands (Mallory et al. 1994, Spitzer to a heavily degraded, extensively open water habitat after and Danks 2006). Relatively few wetland studies have been approximately two and a half years. Here we report on