Peipoch, M., F.R. Hauer, and H.M. Valett

University of MontanaDivision of Biological Sciences

Montana Institute on Ecosystems

BIOGEOCHEMICAL VARIATION AMONG AQUATIC HABITATS OF

RIVERINE FLOODPLAINS

Habitat Heterogeneity vs. Niche Diversity

HABITAT HETEROGENEITY

NICHE DIVERSITYBIODIVERSITY

ECOSYSTEMFUNCTION

Physical Heterogeneity Increases Biofilm Resource Useand Its Molecular Diversity in Stream MesocosmsSinger et al. 2012

Flow heterogeneity

C u

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Ecology’s most general, yet protean pattern: the species-area relationship

Lomolino 2000

Habitat area

Sp

ec

ies

Ric

hn

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s

Biodiversity improves water quality through niche partitioning

Cardinale 2011

Species richness

NO

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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

MilkMissouri

TongueBig horn

Big hole

Swan

Runs

Floodplain aquatic habitats

Parafluvial springbrooks

Backwaters

Orthofluvial springbrooks

Ponds

Flow channels

Pools

Shore lineRun

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 WATERS HYPORHEIC WATERS

Biogeochemical variation: Ammonium

NH4 concentration vs. O2 concentration; r = -0.6 , p-value < 0.01

SURFACE WATER HYPORHEIC WATER

Biogeochemical variation: Nitrate

Low NO3- concentration in surface waters despite of high

NO3- concentration in the hyporheic zone

SURFACE WATER HYPORHEIC 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 abundance Chl-a abundance

Ecosystem metabolism among floodplain habitats

Gross Primary Production & Ecosystem Respiration

MCn=4

PSn=2

OSn=3

PNn=4

MCn=4

PSn=2

OSn=3

PNn=4

GPP:ER ratios

MCn=4

All river floodplains

PSn=2

OSn=3

PNn=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 NO3 concentrations, respectively.

General Conclusions