Peipoch, M., F.R. Hauer, and H.M. Valett University of Montana Division of Biological Sciences Montana Institute on Ecosystems BIOGEOCHEMICAL VARIATION AMONG AQUATIC HABITATS OF RIVERINE FLOODPLAINS

Habitat Heterogeneity vs. Niche Diversity HABITAT HETEROGENEITY NICHE DIVERSITY BIODIVERSITY ECOSYSTEM FUNCTION Physical Heterogeneity Increases Biofilm Resource Use and Its Molecular Diversity in Stream Mesocosms Singer et al Flow heterogeneity C uptake Ecology’s most general, yet protean pattern: the species-area relationship Lomolino 2000 Habitat area Species Richness Biodiversity improves water quality through niche partitioning Cardinale 2011 Species richness NO 3 uptake BIOCOMPLEXITY “Michener et al. 2001, Thompson et al. 2001”

Floodplain Complexity Floodplain complexity: ‘a measure of the variation in geomorphic, hydrologic, and biological forms and processes that exist among ecologically distinct habitats of floodplain landscapes’ Stanford et al. 2005

Multi-scale Assessment of Riverscape Complexity (MARC) Project 1.Variation in nutrient concentrations among floodplain aquatic habitats 2.Variation in biomass abundance among floodplain aquatic habitats 3.Quantification of ecosystem metabolism for four critical habitats in riverine floodplains 10 river floodplains across Montana Bitterroot Clark Fork Boulder Madison Milk Missouri Tongue Big horn Big hole Swan

Runs Floodplain aquatic habitats Parafluvial springbrooks Backwaters Orthofluvial springbrooks Ponds Flow channels Pools Shore line Run s Riffles Confluence zones Main channel habitats (n=5 per floodplain, n=3 per habitat) Off-channel habitats (n=5 per floodplain, n=3 per habitat)

Biogeochemical variation among floodplain habitats

SURFACE WATERSHYPORHEIC WATERS Biogeochemical variation: Ammonium NH 4 concentration vs. O 2 concentration; r = -0.6, p-value < 0.01

SURFACE WATERHYPORHEIC WATER Biogeochemical variation: Nitrate Low NO 3 - concentration in surface waters despite of high NO 3 - concentration in the hyporheic zone

SURFACE WATERHYPORHEIC WATER Biogeochemical variation: Soluble reactive phosphorus (SRP)

N:P ratios vs. Chlorophyll

Biogeochemical variation in floodplain habitats Off-channel habitats play a critical role on the niche diversity of river floodplains by generating larger biogeochemical variation Ammonium NitrateDissolved Oxygen Biomass abundanceChl-a abundance

Ecosystem metabolism among floodplain habitats

Gross Primary Production & Ecosystem Respiration MC n=4 PS n=2 OS n=3 PN n=4 MC n=4 PS n=2 OS n=3 PN n=4

GPP:ER ratios MC n=4 All river floodplains PS n=2 OS n=3 PN n=4

Off-channel habitats are responsible for the majority of biogeochemical variation observed in river floodplains. Variation in N:P ratios (i.e., Nitrate) determines Chl-a standing stocks among aquatic habitats of river floodplains. Main-channel habitats are mostly autotrophic environments while off-channel habitats, especially orthofluvial ponds, are principally heterotrophic ecosystems (i.e., ER > GPP). GPP:ER ratios in main-channel and off-channel zones seem to be driven by SRP and NO 3 concentrations, respectively. General Conclusions