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| Titel |
Nutrient limitations to aquatic production along an alluvial groundwater
connectivity gradient in semi-arid northwest Australia |
| VerfasserIn |
Jordan Iles, Neil Pettit, Pauline Grierson |
| Konferenz |
EGU General Assembly 2017
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| Medientyp |
Artikel
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| Sprache |
en
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 19 (2017) |
| Datensatznummer |
250150808
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| Publikation (Nr.) |
 EGU/EGU2017-15316.pdf |
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| Zusammenfassung |
| Primary production of intermittent streams in hot arid regions, such as the geologically
ancient Pilbara region of northwest Australia, is strongly limited by both water and nutrient
availability. Pulses of allochthonous materials can be significant source of nutrients and
carbon during short periods of connected flow. However, during interflow periods, which may
last months to years, surface water retracts to a series of surface disconnected pools, where
hydrological processes including hyporheic exchange and evapo-concentration of
ions are of increasing importance in maintaining bioavailable nutrients for primary
production.
In the Pilbara, the persistence of individual pools during interflow periods is strongly
linked to local topography and connectivity to alluvial groundwater. We might thus expect
that autochthonous production is greater in pools that become disconnected from
groundwater due to increased concentration of nutrients. We thus investigated the
importance of nitrogen (N) and phosphorus (P) limitations on aquatic production along an
alluvial groundwater connectivity gradient. First, we used in-situ bottle incubations
and a 13C-enriched NaHCO3 isotopic tracer to measure rates of charophyte and
phytoplankton production in response to nutrient amendments. Second, we paired a
nutrient diffusing substrata limitation experiment with high performance liquid
chromatography to i) identify which nutrient(s) limit periphyton production, and ii)
how the periphyton community structure changes within pools along the alluvial
gradient.
Charophyte production was 2 mg C g−1 DW h−1 while phytoplankton production was
orders of magnitude less (∼0.01 mg C g−1 DW h−1). Although charophytes showed no clear
respiration response to short-term nutrient addition, productivity was positively
correlated to both charophyte N and P content (R2 = 0.65, p < 0.001 and R2 =
0.41, p < 0.001 respectively). This relationship was stronger in pools which were
disconnected from alluvial groundwater (N: R2 = 0.92, p < 0.001 and P: R2 = 0.77,
p < 0.001). Short-term phytoplankton production was N limited in some pools
(F > 7.6, p < 0.009) but this was not directly linked to alluvial connectivity.
The chemotaxonomic response of periphyton algae to experimental increases of
biologically available N and P showed clear shifts in production and community
composition, with nitrogen additions aiding in production, whilst P additions alone did not
increase production and in some instances inhibited growth of some taxa. Unique
photosynthetic pigment peaks were identified in each sample and matched with published
values. Clearly both N and P, along with alluvial groundwater connectivity, have
significant and complex roles in regulating production in these pools. Altered hydrology
due to changing climate or water abstraction may thus have significant but as yet
poorly understood impacts on the ecological functioning of intermittent streams. |
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