Causes of spatial variation in abundance and diversity of macroinvertebrates in a newly constructed

1
Causes of spatial variation in abundance and
diversity of macroinvertebrates in a newly
constructed wetland receiving urban runoff Daniel
R. Rosauer and Timothy W. Stewart Department of
Natural Resource Ecology and Management, Iowa
State University, Ames, Iowa 50011 dros_at_iastate.ed
u, twstewar_at_iastate.edu

• Introduction
• In 2003, a wetland was constructed to filter
  non-point source pollutants (e.g., nutrients,
  sediments) from urban runoff flowing toward a
  lake that provides an emergency water source for
  the city of Ames, Iowa.
• The capacity of a wetland to remove pollutants is
  determined by its biological components.
• Macroinvertebrates (invertebrates visible to the
  unaided eye) play key roles in absorbing and
  processing pollutants by eating organic matter,
  bacteria and algae, and subsequently being
  consumed by fish and waterfowl.
• In 2004, we began a long-term study of wetland
  function by quantifying factors affecting
  invertebrate abundance and taxonomic composition.

Methods Wetland characteristics (Fig.
1) Constructed October 2003 Location Ada Hayden
Park, Ames, Iowa (42 4 3 latitude, 93 37 35
longitude) Design 3 ponds separated by concrete
weirs Surface area pond 1 0.26 ha, pond 2
1.13 ha, pond 3 0.68 ha Maximum depth 2.5
m Pond age at sampling 256-259 days
(6/29/04-7/2/04) Invertebrate and coarse
particulate organic matter sampling and
processing 6 samples (Fig. 1) Habitat and method
entire water column (range 0.038-0.047 m3) and
top 5 cm of sediments (0.1 m2 benthic surface
area) contained within Hess sampler using 500
mm-mesh net Invertebrates removed from samples
under 10x power abundance expressed as number of
individuals/m2 flat bottom area and number of
individuals/m3 of water Coarse particulate matter
(CPOM) pieces or clumps of live or dead plants gt
2 cm long dried at 60 C Physical, chemical, and
other biological attributes Depth, dissolved
oxygen, pH, temperature, turbidity measured at
each sampling location Minnow traps (24 hours
per sampling location) to quantify relative fish
abundance

• Results
• 22 invertebrate taxa identified (Table 1)
• Total invertebrate abundance (mean /- SE)
  14,318 /- 3,515 individuals/m2
• Invertebrate taxonomic richness 13.5 /- 1.4
  taxa/0.1 m2
• Invertebrate abundance varied among sampling
  locations (Table 1, Fig. 2).
• Total invertebrate abundance and Cladocera
  abundance were negatively related to fish biomass
  (Fig. 2).
• Taxonomic richness and Physidae (snail) abundance
  were greatest in pond 1, and at locations with
  high CPOM abundance (Fig. 1, Table 2).

Table 2. Taxonomic richness and Physidae
abundance as a function of CPOM and pond.
Indicator variables were used to measure
differences in ponds 2 and 3 relative to pond 1
(Fig. 1).
Fig. 1. The wetland consists of 3 ponds. Dots
indicate sampling locations and arrows denote
streamflow to and from the wetland.
J. Davis
N
Fish have invaded the wetland.
Fig. 2. Total invertebrate (a) and Cladocera (b)
abundance relative to fish biomass
Table 1. Invertebrate taxa and their abundance
(number of individuals/m2 bottom area)
Plants are uncommon in this new wetland.
Stratford Landing Elementary School
P. Steinmann
Objectives 1. Determine invertebrate abundance
and taxonomic composition in a new wetland 2.
Identify early causes of spatial variation in
invertebrate abundance and diversity (i.e.,
taxonomic richness)
Common carp (Cyprinus carpio)

• Conclusions
• Due to vagility and a stream discharging into
  pond 1, many taxa colonized the wetland in lt 8
  months.
• Invertebrate abundance was increased by CPOM, but
  reduced by fish (common carp, green sunfish).
• High turbidity, sparse plant growth, and rarity
  of large-bodied invertebrates indicate the
  wetland currently absorbs few pollutants from
  surface water inputs.