Macroinvertebrate Response to a Gradient of Hydrologic Connectivity within the Lower Mississippi River and Its Floodplain AUDREY B HARRISON, CLIFFORD A OCHS, WILLIAM T SLACK, K JACK KILLGORE, CATHERINE E MURPHY
Hydrologic Connectivity Floodplain Water Bodies Secondary Channels
Water body Classification
LMR BATTURE HABITATS High Connectivity Low connectivity
What are the effects of hydrologic connectivity on biota?
Benthic Macroinvertebrates Relatively immobile Year-round residents Habitat specialists Specific environmental requirements Most lifespans = 1 year Occupy many functional and trophic niches Integral in riverine food web
Study Area All water body types sampled seasonally (4 times per year) One sampling year (Fall 2014- Summer 2015)
Methods Modified Benthic Sled Petite Ponar Grab Ekman Grab
Methods Benthic Sled Ponar Harrison et al., in peer review
Represented Taxa Phylum/ Order/ Families Genera Total Number (sub)class Superorder of Individuals Insecta Ephemeroptera 6 8 111 Trichoptera 5 8 170 Diptera 5 8 5243 Odonata 3 3 19 Coleoptera 2 2 2 Hemiptera 1 1 2 Crustacea Amphipoda 2 2 53 Decapoda 1 1 34 Mysidacea 1 1 2 Isopoda 1 1 11 Ostracoda 1 1 122 Copepoda 1 1 967 Cladocera 1 1 2 Acari 1 1 7 Bivalvia 3 3 164 Gastropoda 2 2 20 Annelida >4 >4 1956 TOTAL: >40 Families >48 Genera 8885
Terrestrial Insect Undetermined Polycentropus Brachycera Chironomidae Pupae Cercobrachys Bivalvia (Crushed) Chironomidae Larvae Limpet Tortopsis Ephemeroptera Undetermined Gammaridae Undetermined Corbicula Pentagenia Corophiidae Amercaenis Gammarus Brachycentridae Undetermined Potamyia Apocorophium Leptoceridae Undetermined Caenidae Undetermined Hydropsyche Dromogomphus Hydropsychidae Undetermined Simuliidae egg Hexagenia Orthocladiinae Diptera undetermined Chironominae Heptageniidae Undetermined Pseudiron Bivalvia Palaemonidae Undetermined Nectopsyche Stenelmis Oligochaeta Isopoda Undetermined Hirudinea Copepoda Leptocerus Tanypodinae Acari Gastropoda (Relict) Bivalvia (Relict) Gastropoda Chaoboridae Ostracoda Ceratopogonidae Chaoborus Hydracarina Chironomidae Nematoda Oecetis Corixidae Mysidaceae Orthotrichia Somatochlora Stratiomyidae Ostracoda (Dead) Sphaeriidae Peltodytes Libellulidae High Connectivity Low connectivity
MRG&P Ecohydrology: Benthic macroinvertebrate assemblages Non-metric MDS Transform: Presence/absence Resemblance: S7 Jaccard 3D Stress: 0.13 SITETYPE FP_LAKE BW_OXBOW BORROW_PIT SEC_CHAN
LMR BATTURE HABITATS High Connectivity Low connectivity
Secondary Channels >100 naturally occurring secondary channels in LMR Occur where river cuts around an island Variable in size, shape, habitat features, and vegetation Often connect river to floodplain
Flow Alteration CLOSURE DIKES placed at upstream end to direct water into main channel Keeps main channel deep enough for navigation Reduces the need for dredging
No Two Channels the Same 17 ft. 16 ft. 20 ft. 19 ft. 20 ft. 17 ft.
Secondary Channel Habitat Utilization
Study Area 9 Secondary Channels 3 Main Channel Sites (Full Connectivity) Sampled High Water (Spring) and Low Water (Fall) Repeated 2 years
Determining Connectivity
1-Jul 15-Jul 29-Jul 12-Aug 26-Aug 9-Sep 23-Sep 7-Oct 21-Oct 4-Nov 18-Nov 2-Dec 16-Dec 30-Dec 13-Jan 27-Jan 10-Feb 24-Feb 10-Mar 24-Mar 7-Apr 21-Apr 5-May 19-May 2-Jun 16-Jun 30-Jun Stage (ft.) Secondary Channel Connectivity 35 MS River Helena, AR (July 2013-July 2014) 30 25 20 15 10 5 0-5 Montezuma Prairie Point Friars Point Isl. 67 Isl. 62 Kangaroo Pt. Ludlow Knowlton Isl. 63 Main Channel LWRP High Connectivity Low connectivity
Represented Taxa Phylum/ (sub)class Order/ Superorder Families Genera Total Number of Individuals Insecta Ephemeroptera 9 12 136 Plecoptera 2 2 5 Trichoptera 2 4 1014 Diptera 4 27 1254 Odonata 2 2 22 Coleoptera 1 1 1 Collembola 1 1 1 Malacostraca Amphipoda 2 2 291 Decapoda 1 1 1 Mysidacea 1 1 7 Maxillopoda Calanoida 1 1 3 Cyclopoida 1 1 52 Branchiopoda Cladocera 1 1 3 Bivalvia Unioidia 1 1 1 Veneroidia 1 1 119 Oligochaeta 2 2 478 TOTAL: 31 Families 59 Genera 3623 Individuals
Taxonomic Richness Results Taxonomic Richness x Stage of Disconnection 30 25 20 Spring 2014 All channels fully connected 15 10 5 0 y = -0.78x + 25.01 R² = 0.66 P<0.001 0 5 10 15 20 25 River Stage of Disconnection (ft.) High Connectivity Low connectivity
Taxonomic Richness 25 Taxonomic Richness x Stage of Disconnection 20 15 Fall 2014 Most channels disconnected, some inaccessible 10 5 0 y = -0.4866x + 17.653 R² = 0.5682 P < 0.001 0 5 10 15 20 River Stage of Disconnection (ft.) High Connectivity Low connectivity
Catch Per Unit Effort 250 CPUE x Stage of Disconnection 200 150 100 y = 0.1125x + 25.478 R² = 0.0003 50 0 0 5 10 15 20 25 River Stage of Disconnection (ft.) High Low Connectivity connectivity
Summary: Most macroinvertebrate taxa are sensitive to any level of connection/disconnection Management: Permanent benthic communities (year-round) Fully Lentic Fully Lotic
Acknowledgements MRG&P ERDC Fish Ecology Team Lauren Leonard Elizabeth Coleman Images: ERDC Fish Team, Google Maps: Google, USACE, ArcGIS