River Runs Through It. Evaluation of Groundwater and Surface Water Connectivity and its Implication on Riparian Biogeochemistry and Ecology
Julian, P 1, G. Fletcher2, A.L. Wright1.
Affiliations:
1 University of Florida, Soil and Water Sciences, Ft. Pierce, Florida, USA. 
2 Wimmera Catchment Management Authority, Horsham, Victoria, AUS 
Thank you for visiting this page, information presented here is intended to supplement the poster presentation of the same name presented at the 12\(^{th}\) International Symposium on Biogeochemistry of Wetlands.
Abstract
Alteration to the hydrologic balance of a river ecosystem can have profound effects on its biogeochemistry and subsequent ecology. Land use conversion, changes in water demand for agricultural and domestic uses and alteration of native vegetation are contributing factors to stream and river hydrology and can resulting in changes to regional groundwater elevations. This altered hydrology can result in surface water salinization through the transport of saline groundwater, accumulation of salts in soils, passive run-off and direct discharge of saline groundwater to surface waters. Stratified pools of saline water can occur due to reduced surface water flow in combination with groundwater discharge of saline water resulting in negative ecological impacts. Salinization of freshwater streams and rivers have been observed across the globe, however most notably salt-affect rivers and streams occur throughout large areas of south-eastern Australia especially in the lower plains in northern and western Victoria, Australia.
This study evaluated the change of water management and regional hydrology relative to surface water salinization and its effect on biota and biogeochemistry within the lower Wimmera River. The lower Wimmera River has a high environmental value with large stretches of intact riparian and in-stream vegetation and many threatened fauna species of concern. The rainfall-runoff relationship along different reaches of the lower Wimmera River have changed over time due to changes in climate and flow regulation by dams and weirs. Changes in water management through the provision of environmental flows has significantly reduced the extent and duration of high salinity events at key locations along the lower reaches of the river. Furthermore, concurrent with reduced salinity events, nutrient concentrations within the river have begun to decline. In addition to improve water quality fish and macroinvertebrate communities have rebounded.
Long term ecological monitoring has demonstrated that flow and water quality issues are critical factors that influence the overall ecological integrity of the Wimmera River. While some argue that environmental flows in lowland rivers are insufficient to adequately reduce harmful ecological impacts, environmental flow management is the central tenant to restoring water quality and ecological health in the River. Since the creation of water savings to be provided as environmental flows in the early 2000’s environmental conditions have improved. Within a decade the River has improved from a highly impacted ecosystem to a highly valued ecosystem and environmental asset within a decade as a direct result of the implementation of environmental flow restoration.
The figure below, illistrates some of the major causes of saliniation in Australian dryland argicultural areas as depicted by Williams (2001). Numerous factors can cause salination of surface waters including catchment (watershed) clearance and irrigation resulting in a rise of subsurface saline aquifer and ultimately seep into surface waters.
The figure below from Western et al. (1996) illustrates the flow of water associated with saline pools. During periods of low flow, saline groundwater seeps into the stream and collects in depressions (low spots) in the streambed. Any freshwater flowing down the river during these periods flows over the top of the saline layer due to differences in density, simialr to salt wedge transport in estuarine ecosystems. Advective transport of saline water can also accumulate in streambed depressions. Typically due to the sheltered nature of the stream due to stream bank slope and vegetation density, wind is unlikely to cause sufficient mixing to adequately mix fresh and saline waters.
Introduction
Water is a vitally important resource for both the natural ecosystem and human livelihoods. Therefore, understanding the quality, quantity and timing of water is essential to provide sustainable water management for both the natural and human system. As a result of anthropogenic pressure and landscape scale modifications (Milly et al 2008) sustainable water management is needed to ensure that the natural ecosystem can be sustainably balanced with the human need for flood protection and consumptive use (i.e. drinking and irrigation) against the need of the ecosystem (Pahl-Wostl 2006). Unregulated flow to riverine and floodplain ecosystems can be highly dynamic with numerous spatial and temporal complexities. River flows ultimately determine the distribution pattern of the main channel, backwater swamps, ephemeral wetlands and tributaries that together make up the entirety of the floodplain. As flow enters riverine floodplains it carries with it sediment, organic matter and nutrients from upstream water bodies stimulating microbial communities and biogeochemical cycling (Heiler et al 1995). Due to watershed alterations, the subsurface saline aquifer can rise and ultimately seep into surface waters. In times of low flow this exchange is exacerbated resulting in prolonged salinization with detrimental effects to the ecosystem.
The objectives of this study was to evaluated hydrologic and water quality conditions within the lower reaches of the Wimmera River. More specificly:
- Evaluate rainfall and discharge relationships along the lower reaches of the Wimmera River.
- Evaluate river salinity (specific conductance) and determine how faunal composition changes due to high salinity conditions.
- Investigate nutrient trends in the Wimmera River.
Methods
Study Area
The Wimmera River is located in northwestern Victoria Australia (Fig 1). The Wimmera River, the largest Victorian river that doesn’t flow to the ocean orginates in the Grampians range in the south-east, meanders north and terminates at Lake Hindmarsh. The Wimmera basin covers approximately 10% of Victoria’s total area with a dominate agriculture land use (Western et al 1996; Lind et al 2007). Approximately 85% of the native vegetation in the basin has been cleared for grazing and broad arce cropping contributing to salinity issues in certain reaches of the river (Lind et al 2006). The flow regime in the Wimmera River is seasonal and highly variable with a total catchment areas of 4,066 km\(^2\) at Horsham. The river recieves an environmental flow allocation from October to May to protect the river from salinisation and other impacts (Lind et al 2006).
Extra Information
More information related to the Wimmera River Basin and the Wimmera Catchment Management Authority can be found at http://www.wcma.vic.gov.au.
Produced in 2006 this short video focusses on how Wimmera CMA manages looks after the Wimmera catchment (watershed) and manages the waterway with environmental water releases. Since the video’s production, construction of the Wimmera-Mallee pipeline has been completed allowing for more security for environmental water releases. Feel free to visit the Wimmera CMA YouTube Channel for more videos of the Wimmera basin.
Interactive Map
Explore the Wimmeria river basin with an interactive map.
Data Sources
Hydrologic Data
Hydrologic data were queried from the Victoria State Government Department of Environment, Land, Water and Planning (DELWP) water measurement information system (WMIS; http://data.water.vic.gov.au). Hydrologic parameters include discharge and water level, typically both data types were available at most monitoring locations. Hydrologic monitoring locations within the area of interest (AOI) identified by Fig 1 that were locationed within the Wimmera River or locations near the confluence of major tributaries of the Wimmera river (i.e. Norton and MacKenzie Creeks) were considered. All available data including discharge and water level was considered between water year 1920 and 2016 (WY; June 1st 1919 and May 30th 2016). Rainfall data were queried from the Australian Government Bureau of Meteorology (BoM) environmental information explorer (http://www.bom.gov.au/jsp/eiexplorer/). Using the same AOI and perod of record (POR) for the hydrologic data query, rainfall monitoring locations were identified along the Wimmera River and within its drainage basin. Furthermore, additional sites were identified in the vaicinity of of Lake Albacutya.
Water Quality Data
Water quality data was retrieved from the DELWP WMIS for monitoring locations along the Wimmera River and tributaries (Fig 1). Additional water quality data was provided by the Environmental PRotection Authority Victoria (EPA Victoria). Both grab samples and in-situ data collected via water quality sonde (i.e. multimeter) were used to characterize water quality within the river. Parameters considered in this analysis included total phosphorus (TP), soluble reactive phosphorus (SRP; also refered to as Filterable Reactive Phosphorus), total nitrogen (TN), nitrate-nitrite (NOX), total suspended solids (TSS) and specific conductance (SPC). All available data was considered between WYs 1990 and 2016. All laboratory analyses were performed consistent with agency approved methods. Data were screened based on laboratory qualier codes and any data associted with a fatal qualifer indicating a potential data quality problem was removed from the analysis. For purposes of data analysis and summary statistics, data reported lass than the method detection limit (MDL) were assigned a value equal to the MDL, unless otherwise noted.
Macroinvertebrate Data
Macroinvertebrate abundance data were provided by EPA Victoria. Samples were collected and analyzed consistent with EPA Vicotira rapid bioassessment methodology (Environmental Protection Authority Victoria 2003).
Data Analysis
Annual discharge and rainfall totals were calculated for each monitoring location consistent with the Victoria WY (June - May). Drough severity was assessed between WY1920 and 2016 using the standardized rainfall anomaly (SRA) index (Agnew and Chappell 1999; Asfaw et al 2018) where the total annual rainfall (Pr) is related to the POR mean and standard devication (Pm and \(\sigma\), respectively) consistent with the equation below. Drought severity can be delineated as extreme (SRA <-1.65), severe (-1.28 > SRA >-1.65), moderate (-0.84 >SRA > -1.28) and no drough (SRA > -0.84) consistent with prior studies (Agnew and Chappell 1999; Asfaw et al 2018).
\[SRA_{t}=\frac{P_{t}-P{m}}{\sigma}\]
Daily average specific conductance was calculated from high-intensity in-situ mointoring data collected at several locations along the Wimmera River (Fig 1) and qualitatively compared to water level data. Annual (WY) arithmetic mean TP, TN and TSS concentrations were computed for monitoring locations with greater than four samples per year. Annual mean TP, TN and TSS concnetration trends were analyzed using Kendall’s tau (\(\tau\)) trend analysis (‘base’ R-package) for sites with adequate data. Macroinvertebrate salinity sensitivity index (SSI) was calculated for each sample consistent with Horrigan et al. (2005). Shannon (H’) and Simpson (1-D) diversity indices were also calculated for each sample using the ‘diversity’ function in the ‘vegan’ R-package (Oksanen and Guillaume 2018). Only sites with greater than two years of data and concurrent water quality monitoring was considered for further analysis. Specific conductance and SSI were compared using Spearman’s correlation (‘base’ R-package). Diveristy indices and SSI were also compared using Spearman’s correlation (‘base’ R-package). All statistical operations were performed with R (Ver 3.1.2, R Foundation for Statistical Computing, Vienna Austria), unless otherwise stated all statistical operations were performed using the base R library. The critical level of significance was set at \(\alpha\) = 0.05.
Results
| Region | Thiel-Sen’s Slope | \(\tau\)-value | \(\rho\)-value |
|---|---|---|---|
| Long Term (1920 - 2016) | |||
| Albacutya | -1.6 | -0.27 | <0.01 |
| Hindmarsh | -1.5 | -0.25 | <0.01 |
| Quantong | -0.9 | -0.15 | <0.05 |
| Horsham | 0.5 | 0.09 | 0.23 |
| Short Term (1990 - 2016) | |||
| Albacutya | -5.1 | -0.36 | <0.05 |
| Hindmarsh | -4.1 | -0.37 | <0.01 |
| Lochiel | -3.7 | -0.90 | <0.05 |
| Dimboola | -4.5 | -0.26 | 0.06 |
| Quantong | -6.6 | -0.42 | <0.01 |
| Horsham | -3.3 | -0.25 | 0.06 |
Extra Information
- Macroinvertebrate SSI was negatively correlated with surface water specific conductance (N=68, r-value=-0.33, \(\rho\)-value<0.05)
- Macroinvertebrate SSI was positively correlated with Shannon’s diversity index (N=68, r-value=0.45, \(\rho\)-value<0.01)
Extra Information
Comparison of Shannon diversity index (H’) between sites along the Wimmera River. Letters indicate statistically significant differences between sites assess by Dunn’s test of multiple comparisons. Overall Shannon diversity index was statistically different between sites (\(\chi^{2}\)=33.5, df=4, \(\rho\)-value=<0.01)
Comparison of Simpson (1-D) diversity index between sites along the Wimmera River. Letters indicate statistically significant differences between sites assess by Dunn’s test of multiple comparisons. Overall Shannon diversity index was statistically different between sites (\(\chi^{2}\)=33.1, df=4, \(\rho\)-value=<0.01)
| Area1 | TP (\(\mu\)g L-1) | SRP (\(\mu\)g L-1) | TN (mg L-1) | NOX (\(\mu\)g L-1) | SPC (\(\mu\)S cm-1) | TSS (mg L-1) |
|---|---|---|---|---|---|---|
| Jeparit | 157.4 \(\pm\) 40.5 | 3.6 \(\pm\) 1.18 | 38 \(\pm\) 0.015 | 50171 \(\pm\) 9797 | 14.5 \(\pm\) 3.8 | |
| (16 - 820; 25) | (0.8 - 16; 14) | (3 - 370; 25) | (1790 - 110374; 15) | (7 - 40; 8) | ||
| Tarranyurk | 31.3 \(\pm\) 7.9 | 1.2 \(\pm\) 0.1 | 24 \(\pm\) 0.021 | 45313 \(\pm\) 3126 | ||
| (5 - 74; 8) | (0.9 - 1.4; 4) | (3 - 170; 8) | (29930 - 55601; 8) | |||
| Lochiel | 45.1 \(\pm\) 2.5 | 6.9 \(\pm\) 0.8 | 1.2 \(\pm\) 0.03 | 31 \(\pm\) 0.004 | 3020 \(\pm\) 138 | 17.3 \(\pm\) 0.8 |
| (7 - 300; 319) | (1 - 150; 311) | (0.5 - 3.8; 315) | (2 - 510; 319) | (359 - 21740; 316) | (2 - 120; 311) | |
| Dimboola/Big Bend | 36.1 \(\pm\) 6.6 | 1.4 \(\pm\) 0.2 | 8 \(\pm\) 0.004 | 14070 \(\pm\) 3655 | ||
| (16 - 74; 9) | (0.8 - 1.7; 3) | (3 - 41; 9) | (20200 - 65300; 2) | |||
| Dimboola | 50.6 \(\pm\) 7.5 | 17.4 \(\pm\) 12.5 | 1.1 \(\pm\) 0.03 | 46 \(\pm\) 0.008 | 41750 \(\pm\) 22550 | 14.2 \(\pm\) 1.4 |
| (8 - 1000; 176) | (3 - 1000; 80) | (0.5 - 2.9; 174) | (3 - 1000; 176) | (20200 - 6350000; 2) | (1 - 140; 171) | |
| MacKenzie | 79.0 \(\pm\) 5.6 | 9.0 \(\pm\) 1.7 | 1.3 \(\pm\) 0.05 | 32 \(\pm\) 0.007 | 244 \(\pm\) 21 | 16.5 \(\pm\) 1.3 |
| (12 - 490; 192) | (3 - 250; 192) | (0.5 - 4.2; 192) | (2 - 760; 192) | (95 - 2238; 135) | (1 - 150; 192) | |
| Horsham | 54.4 \(\pm\) 2.1 | 6.0 \(\pm\) 0.4 | 1.1 \(\pm\) 0.02 | 55 \(\pm\) 0.005 | 1490 \(\pm\) 36 | 20.5 \(\pm\) 1.2 |
| (5 - 210; 339) | (3 - 60; 339) | (0.01 - 3.0; 339) | (2 - 800; 339) | (216 - 4127; 337) | (1 - 180; 339) | |
| Horsham/Walmer | 34.8 \(\pm\) 5.0 | 0.8 \(\pm\) 0.07 | 11 \(\pm\) 0.005 | 987 \(\pm\) 174 | ||
| (22 - 45; 4) | (0.75 - 0.88; 2) | (3 - 22; 2) | (607 - 1528; 5) | |||
| Area | Site ID | Source |
|---|---|---|
| Jeparit | 141900 | EPA Victoria |
| Jeparit | 154300 | EPA Victoria |
| Tarranyurk | 415247 | EPA Victoria |
| Lochiel | 142100 | EPA Victoria |
| Dimboola/Big Bend | 141540 | EPA Victoria |
| Dimboola | 154500 | EPA Victoria |
| Lochiel | 415246 | DELWP |
| MacKenize | 415251 | DELWP |
| Horsham | 415200 | DELWP |
| Horsham/Walmer | 154600 | EPA Victoria |
.
Conclusions
- Rainfall patterns have significantly declined in several regions of the Wimmera river across the long (96 year) and medium (26 year) term period potentially indicating a shift in regional climate (Fig 2).
- Using the SRA index flood and drought periods can be identified, several drought periods were identified including the World War II (1939 – 1946) and Millennial (2001 – 2009) drought and flood years (i.e. 1942, 2011, etc.) to name a few (Fig 3 and 4).
- Specific conductance values vary dramatically along the lower reaches of the Wimmera River (Fig 5 and Table 2).
- River water level generally corresponds with high salinity (specific conditions) especially in the lower reaches (i.e. Tarranyurk; Fig 5).
- Periods of high salinity within the river influences macroinvertebrate diversity. As expected, opportunistic taxa (less salinity sensitive species) were present at both impacted and unimpacted sites while high salinity sites corresponded with lower diversity (Fig 6 and 7).
- Generally, total nutrients concentrations have remained constant with low inorganic nutrient concentrations. Suspended solids were variable across the network with some sites experiencing significant declines in concentrations (Fig 8).
Extra Information
Acknowledgements
We would like to thank the Victoria State Government and the Environmental Protection Authority Victoria for allowing access to the extensive and extremely valuable data collected along the Wimmera River. More specifically I would like to thank Anne-Maree Westbury and her team in providing supplemental water quality and macroinvertebrate data.
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