The influence of a flood event on the potential sediment control of baseflow phosphorus concentrations in an intensive agricultural catchment
The growth of periphyton in streams is enhanced by phosphorus (P) in baseflow. The likely control of P concentrations in baseflow can be approximated by the equilibrium P concentration (EPC0) of bed sediments. However, sediment composition changes with spatial scale and flood events. It is unknown if this affects EPC0.
Materials and methods
We sampled sediments in a main stem and headwater tributary of an agricultural catchment in Reporoa, New Zealand, before and after a scouring flood event (99th percentile of flows recorded since 1962). The tributary was chosen for its low slope and predominantly single land use (intensive dairying), which minimised the number of factors likely to affect the influence of the storm event.
Results and discussion
EPC0 values were significantly correlated to dissolved reactive P (DRP) in baseflow before, and after, the flood event, despite a decrease in the proportion of fines and total P in bed sediments. Both EPC0 and DRP concentrations increased towards the catchment outlet. This increase likely reflected new P-enriched sediments from dairy-farm runoff, but hyporheic zone samples suggested that shallow groundwater may also have played a role in supplying P to the water column. Despite diel variations in dissolved oxygen, DRP concentrations showed little variation during the day and matched EPC0 estimates.
This work suggests that despite changes in sediment composition due to flood events, EPC0 is a useful reflection of daytime baseflow-DRP concentrations at sites along a stream network. However, further work is required to clarify if sediment-P exchange or groundwater control baseflow-DRP concentrations. These data also inform our understanding of the influence of sediment on delaying farm and catchment efforts to decrease in-stream DRP concentrations.
KeywordsAnaerobic Flood Groundwater Hyporheic Runoff
We thank Brian Moorhead, Tasman McKelvey, Aldrin Rivas, and Kerry Costley for assisting with field work, in particular, deployment and operation of the automated samplers and water quality sondes. We also acknowledge the cooperation of local farmers for site access.
This work was funded by the New Zealand Ministry for Business, Innovation and Employment’s Transfer Pathways Programme (contract LVLX1502-CR-2) and the Our Land and Water National Science Challenge (contract C10X1507).
- APHA-AWWA-WEF (2005) Standard methods for the examination of water and wastewater. American Public Health Association, American Water Works Association, and Water Environment Federation, Washington DCGoogle Scholar
- Einsele G (2013) Sedimentary basins: evolution, facies, and sediment budget. Springer Science & Business Media, Heidelberg, GermanyGoogle Scholar
- Gee GW, Bauder JW (1986) Particle-size analysis1. In: Klute A (ed) Methods of soil analysis: part 1—physical and mineralogical methods. SSSA Book Series Soil Science Society of America, American Society of Agronomy, Madison, WI, pp. 383–411Google Scholar
- Genstat Committee (2015) Genstat v17.0. VSNI, Hemel Hempstead, UKGoogle Scholar
- Hewitt AE (2010) New Zealand soil classification. Landcare Research Science Series. Manaaki Whenua Press, Landcare Research, Lincoln, pp. 136Google Scholar
- Jensen MB, Hansen HCB, Nielsen NE, Magid J (1998) Phosphate mobilization and immobilization in two soils incubated under simulated reducing conditions. Acta Agric Scand Sect B Soil Plant Sci 48:11–17Google Scholar
- Lucci GM, McDowell RW, Condron LM (2010) Evaluation of base solutions to determine equilibrium phosphorus concentrations (EPC0) in stream sediments. Int Agrophys 24:157–163Google Scholar
- McDowell RW (2015) Relationship between sediment chemistry, equilibrium phosphorus concentrations, and phosphorus concentrations at baseflow in rivers of the New Zealand National River Water Quality Network. J Environ Qual 44Google Scholar
- Olsen SR, Cole CV, Watanbe FS, Dean LA (1954) Estimation of available phosphorus in soils by extraction with sodium bicarbonate, United States Department of Agriculture. Circular No. 939. U.S. Dept. of Agriculture, Washington, D.C., pp. 19Google Scholar
- Piper J (2005) Water resources of the Reporoa Basin. Environment Waikato Regional Council, Hamilton, New ZealandGoogle Scholar
- Taylor MD, Mulholland M, Thirnburrow D (2009) Infiltration characteristics of soils under forestry and agriculture in the upper Waikato catchment. Environment Waikato Regional Council, Hamilton, New ZealandGoogle Scholar