How do Water Regime and Grazing Alter the Reproductive Capacity of Aquatic Plants?
Dr Margaret A. Brock
Botany, Rural Science and Natural Resources,
University of New England
Environment Australia, 2000
Attachment E
Physico-chemical Water Quality of the UNE Experimental Wetlands
Sue Botting and Laurie O'Donnell
Introduction
The University of New England Experimental Wetlands are supplied by water from a nearby creek (Duval Creek). The water fed into the ponds varies in volume and quality depending on the artificial regime imposed and the quality of the water in Duval Creek. Water quality within ponds may also be affected by vegetation composition, faunal influences (e.g. nesting ducks) and the microclimate of the wetland.
A long-term program has been undertaken since September 1997 to monitor water quality within the UNE Experimental Wetlands. This has been supplemented since September 1999 with sampling for additional parameters within the wetlands and along Duval Creek.
Aims
The aims of the water quality monitoring program have been identified as:
- Identify long-term or seasonal trends across all wetlands
- Compare water chemistry between regimes
- Compare water chemistry within regimes (i.e. identify differences between wetlands)
- Compare water chemistry upstream and downstream of wetlands in Duval Creek
Methods
Long-term water quality monitoring program:
Testing began in approximately September 1997 and has continued through to June 2000.
A Hydrolab MiniSonde probe is lowered into the deep end of each wetland until it touches the duckboard. A light excluding device has been used to cover the probe since spring 1999. Readings are given by the Surveyor 4 data display. Parameters measured include:
- Conductivity (mS/cm)
- Turbidity (NTU)
- Temperature (°C)
- pH
- Dissolved oxygen (mg/L)
A secchi disk reading is also taken for each wetland.
Supplementary water quality monitoring program:
Testing began in September 1999 and has continued through to June 2000.
Sample locations:
- 2 sites in Duval Creek downstream of wetlands
- 2 sites in Duval Creek upstream of wetlands
- each wetland in the central deep section
Parameters measured include:
- Conductivity (mS/cm)
- Turbidity (FTU)
- Temperature (°C)
- pH
- Dissolved nitrite-nitrate (mg/L)
- Soluble reactive phosphorus (mg/L)
A TPS MC-81 water meter was used to measure pH, temperature and conductivity. Three replicate water samples were collected for analysis in the laboratory for turbidity, dissolved nitrite-nitrate (NOx) and soluble reactive phosphorus (SRP). Samples for turbidity were measured on a Hanna Portable Microprocessor Turbidity Meter HI93703 meter. Dissolved nitrite-nitrate and soluble reactive phosphorus samples were filtered and then analysed using the cadmium reduction and molybdate blue methods, respectively.
Results and Interpretive Notes
Initial interpretations are derived using EDA and addressing four aims as noted above.
Conductivity (Figure e1)
- Are some general longterm trends followed by all regimes:
- Increase in conductivity over summer and autumn of 1997/98 (water inputs from creek + evaporation = increased concentration of salts)
- Decrease in conductivity during spring 1998 (high rainfall period diluting salts in ponds)
- Increase in summer 1998/99
- Decrease in autumn 1999
- General increase since then with occasional seasonal falls
- => Seasonal trends relating to warm dry weather + evaporation concentrating salts and periods of rain diluting them.
- Regimes fairly closely matched. Permanent regime has slightly higher mean than other regimes (not flushed as often).
- Wetlands within regimes fairly consistent
- Wetland 1 (Spring) is generally higher than other spring wetlands
- No differences between up and downstream Duval Creek
Turbidity (Figure e2)
- Long-term trends for all wetlands not obvious
- Differences of note between regimes
- Permanent wetlands consistently low turbidity
- Autumn, Twice fill and Mimic regimes show some similar peaks and troughs since spring 1998
- Spring fill shows more variability
- Turbidity levels within regimes (between wetlands) are very similar
- No differences between up and downstream Duval Creek
Temperature (Figure e3)
- All wetlands show seasonal trends of warming over summer and cooling over winter
- Very little difference between regimes
- Wetlands within regimes are also similar
- No differences between up and downstream Duval Creek
pH (Figure e4)
- Slight long-term increase in pH leveling out around summer 1998/99
- Are some differences between regimes
- Permanent wetlands generally higher pH than other regimes
- Spring regime peaks occur in autumn (wetland is emptying)
- Consistent pattern within regimes
- No differences between up and downstream Duval Creek
Dissolved oxygen (Figure e5)
- Are general long-term trends across all ponds
- Fairly steady decline in DO from spring 1998 to autumn 1999
- Increase from autumn 1999 to summer 1999/2000
- Several peaks evident: July 1998, October 1998, June 1999 and December 1999
- No apparent differences between regimes
- Consistent pattern within regimes
- Dissolved oxygen not measured for Duval Creek
Secchi disk
- Long-term data highly variable
- Some obvious differences between regimes
- Permanent wetlands have consistently high secchi readings
- Twice annual fill secchi fluctuates in response to filling
- Autumn and spring fills also fluctuate - possibly in response to fill but not a consistent pattern
- Similar patterns of secchi readings within regimes (between wetlands)
- Secchi disk not measured for Duval Creek
Dissolved nitrite-nitrate
- Long-term data not collected
- For period of collection (Sept 1999 - May 2000) NOx levels are considered to be low
- No apparent differences between regimes
- Similar variability within regimes as between them
- No differences between up and downstream Duval Creek
Soluble reactive phosphorus
- Long-term data not collected
- For period of collection (Sept 1999 - May 2000) SRP levels are considered to be low
- Compare water chemistry between regimes
- Similar variability within regimes as between them
- No differences between up and downstream Duval Creek
Key
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