During periods of low river discharge, bacterial growth is typically limited by dissolved organic... more During periods of low river discharge, bacterial growth is typically limited by dissolved organic carbon (DOC) and is tightly regulated by phytoplankton production. However, import of allochthonous DOC into rivers by freshwater inflows may diminish bacterial reliance on phytoplankton-produced carbon, leading to competition for nitrogen (N) and phosphorus (P). To investigate phytoplankton–bacterial competition in response to allochthonous inputs, we conducted a mesocosm experiment, comparing microbial responses to the following two manipulation treatments: (1) addition of N and P, and (2) addition of a DOC and N and P. Measurement of chlorophyll-a estimated phytoplankton biomass and microscopic counts were performed to discriminate community change. Bacterial abundance was tracked using flow cytometry and community assemblages were characterised using automated ribosomal intergenic spacer analyses and 16S rRNA-amplicon sequencing. We found that bacterial abundance increased in the le...
Australasian Journal of Environmental Management, 2015
ABSTRACT Understanding longitudinal variation in water quality along rivers and how they are infl... more ABSTRACT Understanding longitudinal variation in water quality along rivers and how they are influenced by large dams is important for both ecological theory and river management. This study examines longitudinal changes in water quality downstream of a large bottom release dam (Lake Copeton) on the Gwydir River, Australia. We compared longitudinal changes in water quality variables from sites upstream and downstream of Lake Copeton over a two-year period and a total river distance of approximately 200 km. Lake Copeton acted as a source of nitrogen as nitrogen oxides (NOx) and phosphorus as filterable reactive phosphorus (FRP). A significant increase in the concentration of NOx and FRP was evident downstream of the dam, particularly in summer with elevated concentrations detected up to 60 km downstream. Significantly lower chlorophyll a (Chl-a) concentrations and electrical conductivity (EC) were evident below the dam. Mean nutrient concentrations declined with increased distance downstream of Lake Copeton while Chl-a concentrations increased, suggesting uptake by autotrophs. This study suggests that Copeton Dam disrupts the river continuum for nutrients, Chl-a and EC as predicted by the serial discontinuity concept, with recovery occurring approximately 60 km downstream.
The relationships between discharge and dissolved organic carbon (DOC) have been extensively stud... more The relationships between discharge and dissolved organic carbon (DOC) have been extensively studied in rainfall runoff-driven stream systems. Less is known about discharge and DOC relationships in river systems dependent on floodplain inundation. We examined DOC dynamics and mobilisation over low discharge periods and several larger discharge events in the highly regulated lowland Namoi River, Australia. Stable isotope signatures (δ13C) of various water-column fractions (e.g. 200 µm, fine particulate organic matter) were used to determine the sources of DOC. DOC concentrations over low discharge periods were fairly similar among sites and ranged between 5 and 10 mg L–1. Concentrations during a high-discharge event increased substantially with a mean of 20.4 mg L–1 and a maximum of 44 mg L–1. Significant positive linear relationships were found between DOC concentrations and discharge (P < 0.001, r2 = 0.45). The 13C composition of DOC sampled across the three sites (e.g. –26.2‰) ...
ABSTRACT Diel variation in dissolved organic carbon (DOC) within lotic systems has been reported ... more ABSTRACT Diel variation in dissolved organic carbon (DOC) within lotic systems has been reported on numerous occasions. However, to our knowledge there has been no published work on diel DOC variation within lowland rivers during high flow events. We sampled DOC at 4 h intervals from two sites across two distinct flow regimes in the regulated lower Namoi River, Australia. This included a large flood (mean flow 224 m3 s−1 and a peak flow of 376 m3 s−1) sampled every 4 h for 10 consecutive days. DOC concentrations were significantly greater at night than during the day (P &lt; 0.05) and the mean DOC concentration was 23.4 mg L−1 at night compared to 18.9 mg L−1 during daylight hours. The magnitude and duration of flow within this lowland river system and the mobilisation of large quantities of allochthonous carbon appeared to play a role in increasing DOC concentration and the diel difference.
Stable isotope signatures (δ13C and δ15N) were used to compare trophic linkages between epilithic... more Stable isotope signatures (δ13C and δ15N) were used to compare trophic linkages between epilithic periphyton and three families of macroinvertebrates (Baetidae, Leptophlebiidae and Gripopterygidae) in riffles of two rivers with developed catchments (including agriculture, urbanization, impoundment and flow regulation) and two with undeveloped catchments (native forest with no major impoundments) in the Murrumbidgee River system, New South Wales, Australia. Periphyton
The IMEF project was initiated and implemented by Dr Penny Knights, DLWC Sustainable Water Manage... more The IMEF project was initiated and implemented by Dr Penny Knights, DLWC Sustainable Water Management Division, with the assistance of Dr Tony Church (EPA), Marie Egerrup, Dr Simon Mitrovic and Andrew Sedger. Dr Barbara Downes (University of Melbourne) provided an ...
... SM Mitrovic (*) .DP Westhorpe NSW Office of Water, PO Box 3720, Parramatta 2124 NSW, Australi... more ... SM Mitrovic (*) .DP Westhorpe NSW Office of Water, PO Box 3720, Parramatta 2124 NSW, Australia e-mail: simon.mitrovic@dnr.nsw.gov.au ... Some studies consider bacterial carbon pools a minor source of carbon for higher trophic levels (Sobczak et al. ...
... SM Mitrovic (*) .DP Westhorpe NSW Office of Water, PO Box 3720, Parramatta 2124 NSW, Australi... more ... SM Mitrovic (*) .DP Westhorpe NSW Office of Water, PO Box 3720, Parramatta 2124 NSW, Australia e-mail: simon.mitrovic@dnr.nsw.gov.au ... Some studies consider bacterial carbon pools a minor source of carbon for higher trophic levels (Sobczak et al. ...
During periods of low river discharge, bacterial growth is typically limited by dissolved organic... more During periods of low river discharge, bacterial growth is typically limited by dissolved organic carbon (DOC) and is tightly regulated by phytoplankton production. However, import of allochthonous DOC into rivers by freshwater inflows may diminish bacterial reliance on phytoplankton-produced carbon, leading to competition for nitrogen (N) and phosphorus (P). To investigate phytoplankton–bacterial competition in response to allochthonous inputs, we conducted a mesocosm experiment, comparing microbial responses to the following two manipulation treatments: (1) addition of N and P, and (2) addition of a DOC and N and P. Measurement of chlorophyll-a estimated phytoplankton biomass and microscopic counts were performed to discriminate community change. Bacterial abundance was tracked using flow cytometry and community assemblages were characterised using automated ribosomal intergenic spacer analyses and 16S rRNA-amplicon sequencing. We found that bacterial abundance increased in the le...
Australasian Journal of Environmental Management, 2015
ABSTRACT Understanding longitudinal variation in water quality along rivers and how they are infl... more ABSTRACT Understanding longitudinal variation in water quality along rivers and how they are influenced by large dams is important for both ecological theory and river management. This study examines longitudinal changes in water quality downstream of a large bottom release dam (Lake Copeton) on the Gwydir River, Australia. We compared longitudinal changes in water quality variables from sites upstream and downstream of Lake Copeton over a two-year period and a total river distance of approximately 200 km. Lake Copeton acted as a source of nitrogen as nitrogen oxides (NOx) and phosphorus as filterable reactive phosphorus (FRP). A significant increase in the concentration of NOx and FRP was evident downstream of the dam, particularly in summer with elevated concentrations detected up to 60 km downstream. Significantly lower chlorophyll a (Chl-a) concentrations and electrical conductivity (EC) were evident below the dam. Mean nutrient concentrations declined with increased distance downstream of Lake Copeton while Chl-a concentrations increased, suggesting uptake by autotrophs. This study suggests that Copeton Dam disrupts the river continuum for nutrients, Chl-a and EC as predicted by the serial discontinuity concept, with recovery occurring approximately 60 km downstream.
The relationships between discharge and dissolved organic carbon (DOC) have been extensively stud... more The relationships between discharge and dissolved organic carbon (DOC) have been extensively studied in rainfall runoff-driven stream systems. Less is known about discharge and DOC relationships in river systems dependent on floodplain inundation. We examined DOC dynamics and mobilisation over low discharge periods and several larger discharge events in the highly regulated lowland Namoi River, Australia. Stable isotope signatures (δ13C) of various water-column fractions (e.g. 200 µm, fine particulate organic matter) were used to determine the sources of DOC. DOC concentrations over low discharge periods were fairly similar among sites and ranged between 5 and 10 mg L–1. Concentrations during a high-discharge event increased substantially with a mean of 20.4 mg L–1 and a maximum of 44 mg L–1. Significant positive linear relationships were found between DOC concentrations and discharge (P < 0.001, r2 = 0.45). The 13C composition of DOC sampled across the three sites (e.g. –26.2‰) ...
ABSTRACT Diel variation in dissolved organic carbon (DOC) within lotic systems has been reported ... more ABSTRACT Diel variation in dissolved organic carbon (DOC) within lotic systems has been reported on numerous occasions. However, to our knowledge there has been no published work on diel DOC variation within lowland rivers during high flow events. We sampled DOC at 4 h intervals from two sites across two distinct flow regimes in the regulated lower Namoi River, Australia. This included a large flood (mean flow 224 m3 s−1 and a peak flow of 376 m3 s−1) sampled every 4 h for 10 consecutive days. DOC concentrations were significantly greater at night than during the day (P &lt; 0.05) and the mean DOC concentration was 23.4 mg L−1 at night compared to 18.9 mg L−1 during daylight hours. The magnitude and duration of flow within this lowland river system and the mobilisation of large quantities of allochthonous carbon appeared to play a role in increasing DOC concentration and the diel difference.
Stable isotope signatures (δ13C and δ15N) were used to compare trophic linkages between epilithic... more Stable isotope signatures (δ13C and δ15N) were used to compare trophic linkages between epilithic periphyton and three families of macroinvertebrates (Baetidae, Leptophlebiidae and Gripopterygidae) in riffles of two rivers with developed catchments (including agriculture, urbanization, impoundment and flow regulation) and two with undeveloped catchments (native forest with no major impoundments) in the Murrumbidgee River system, New South Wales, Australia. Periphyton
The IMEF project was initiated and implemented by Dr Penny Knights, DLWC Sustainable Water Manage... more The IMEF project was initiated and implemented by Dr Penny Knights, DLWC Sustainable Water Management Division, with the assistance of Dr Tony Church (EPA), Marie Egerrup, Dr Simon Mitrovic and Andrew Sedger. Dr Barbara Downes (University of Melbourne) provided an ...
... SM Mitrovic (*) .DP Westhorpe NSW Office of Water, PO Box 3720, Parramatta 2124 NSW, Australi... more ... SM Mitrovic (*) .DP Westhorpe NSW Office of Water, PO Box 3720, Parramatta 2124 NSW, Australia e-mail: simon.mitrovic@dnr.nsw.gov.au ... Some studies consider bacterial carbon pools a minor source of carbon for higher trophic levels (Sobczak et al. ...
... SM Mitrovic (*) .DP Westhorpe NSW Office of Water, PO Box 3720, Parramatta 2124 NSW, Australi... more ... SM Mitrovic (*) .DP Westhorpe NSW Office of Water, PO Box 3720, Parramatta 2124 NSW, Australia e-mail: simon.mitrovic@dnr.nsw.gov.au ... Some studies consider bacterial carbon pools a minor source of carbon for higher trophic levels (Sobczak et al. ...
Uploads
Papers by Douglas Westhorpe