Quarterly Report
Quarterly Report Reporting period: July 16 – September 30, 2009 Project: Riparian Vegetation Impacts on Water Quantity, Quality, and Stream Ecology Principal Investigators: Durelle Scott, Erkan Istanbulluoglu, John Lenters, and Kyle Herrman Summary Data collection from this growing season was successful and we were able to document two herbicide treatments of Phragmites australis via helicopter. On July 22, 2009 the wetland site just west of Arapahoe, Nebraska was sprayed (Figure 1) and the stream site on the South Channel of the Platte River was sprayed on September 25, 2009 (Figure 2). Analysis is underway to process meteorological data from the Bowen Stations, sensible heat flux values from the large aperture scintillometers (LAS), heat storage terms, and groundwater levels from pressure transducers to estimate evapotranspiration rates within the wetland. For the ecological projects, we have completed sampling and analysis for the biogeochemical study, completed sampling for the carbon dioxide flux chamber study, and collected data for the stream metabolism and water quality experiment along the South Channel of the Platte River. We have also organized a workshop for the model (IBIS) we are utilizing in this project. The IBIS workshop will be held at the University of Wisconsin-Madison from October 21 - 23, 2009. Several research groups from University of Wisconsin, University of Minnesota, Iowa State University, and University of Nebraska-Lincoln are expected to attend. During the workshop, we will develop a new physiological dataset on P. australis for use with IBIS. A new high resolution soil texture data set will also be developed.
Figure 1. Picture showing the helicopter spraying the Phragmites australis within the Arapahoe Wetland on July 22, 2009.
Figure 2. Picture of the helicopter spraying Phragmites australis along the banks of the South Channel of the Platte River on September 25, 2009. Evapotranspiration estimates using meteorological instruments Throughout the summer data has been collected and instruments checked periodically for any problems. As a result of shorter days, the temperature aspirators at the meteorological station in the Cattail have been turned off to conserve power. The large aperture scintillometer (LAS) and the station in the P. australis will continue to run until the beginning of November to get the longest data set possible before the LAS and the station aspirators need to be shut down. The wetland was also mapped with a differential GPS (DGPS), which was measured with sub meter accuracy (Figure 3). Precise measurements were needed to establish an exact distance between the LAS receiver and transmitter to derive sensible heat flux. As the growing season is wrapping up, the data is being analyzed for quality control. Except for a couple of weeks in March/April when a station failed due to insufficient power, we received full data throughout the growing season (Figure 4). We found that the upper temperature sensor at the P. australis site (Bowen 1) was reading erroneous data from June 13th – July 23rd (Figure 5). Since this measurement is used for the Bowen ratio energy balance and the calculation of sensible heat flux from the LAS, it is important to fill in the data gaps with the least amount of error possible. We are also in the process of determining how sensitive the LAS setup is to the inputs of plant height, receiver/transmitter distance, water level, temperature, and relative humidity. Preliminary results have shown that the LAS setup is most affected by plant height. This will help determine how long each time step should be and the statistical error between each derivation of sensible heat flux. Finally we have estimated the Cattail and P. australis plant height throughout the beginning of the growing season (Figure 6). This will help determine the plant height when sensible heat is calculated and also give an illustration of how the two plants have grown with respect of each other.
Figure 3. Aerial image of the wetland overlaid with points taking from a DGPS unit. The yellow circles represent the wetland boundary, the red triangles represent the LAS transmitter (western) and receiver (eastern), and the purple circles are Bowen 1 (western) and Bowen 2 (eastern). The yellow circles that cut across the wetland are the approximate location were the Phragmites australis transition to cattail as you move west to east.
Figure 4. The daily average albedo over Phragmites australis at Bowen 1 and Cattail at Bowen 2. Albedo uses the measurements of incoming shortwave and net shortwave for both stations. This is a good illustration of all the data collected throughout the year.
Figure 5. The average daily upper temperature difference between Bowen 1 (Phragmites australis) and Bowen 2 (Cattail). The period when the difference becomes large is the time when the upper sensor was reading erroneous data.
Figure 6. Estimated plant heights of Phragmites australis and Cattail.
The use of groundwater fluctuations to estimate evapotranspiration The interaction between shallow groundwater and land surface processes (e.g., actual evapotranspiration-ETa) through the mechanisms of capillary rise and groundwater evapotranspiration (ETg) may play an important role in the ecohydrological system, particularly in semi-arid regions with limited water availability. ETg mainly depends upon the depth of groundwater table, soil texture, atmospheric driving power, and surface vegetation cover. In order to quantify the effect of groundwater on ETa in regions with shallow water tables, we modeled evapotranspiration under different depths of groundwater tables, soil textures, and surface cover conditions. To simulate the groundwater influence on ET in the Republican River basin, we chose a HPRCC observation station near Champion, NE to calculate potential ET using the Penman-
Monteith equation under reference ET and bare soil ET conditions for 28 years (1982-2008; Figure 7). A process-based hydrodynamic model, Hydrus-1D, is used in this study (Simunek et al., 2005) which is based on the Richards equation for solving soil moisture flow in porous media. The constant head lower boundary condition is used to represent the groundwater table. The simulation results are plotted in Figure 8. In general, groundwater has a significant impact on surface evapotranspiration. The degree of the impact decreases almost exponentially with increasing water depths. Furthermore, coarser soils tend to have less impact on ETa at the same depth of water table (Figure 8).
Figure 7. Reference ET and potential bare soil ET in Champion station.
Figure 8. Percentage of groundwater contribution on ET for different soil textures, surface covers and groundwater table depths.
Carbon dynamics in an invaded riparian wetland in South-Central Nebraska The field season for 2009 was completed during the first week of October. Since the last quarterly report, 3 more field days have completed as well as a 24-hour run. The following figures represent preliminary results from the study and bars with different letters are statistically different (α = 0.05). Soil respiration was low relative to the other components of the carbon balance with significant differences early in the season (Figure 9) while methanogenesis rates were roughly five times higher than soil respiration rates with similar rates between all three habitat types (Figure 10). NEECarbon was highest in P. australis areas and displayed strong seasonality peaking during late June (Figure 11). NEE of carbon also displayed strong diurnal variation peaking in mid-afternoon; diurnal swings were greatest in P. australis (Figure 12). Although sampling in the field has been completed, all of the data has not been analyzed. We expect to finish laboratory analysis in the coming weeks and final conclusions will be made shortly thereafter. Soil respiration rates were highest in the P. australis areas early in the season, but overall soil respiration does not appear to be a major source of carbon in this environment. On the other hand, methanogenesis was similar between all three habitat types and appears to be the major source of carbon compared to other studies conducted in natural wetlands. This has significant implications, as methane has a global warming potential that is 20 times higher than carbon dioxide. NEECarbon showed significant differences through the first three sampling dates, with P. australis fixing 2-5 times more carbon than open water and native areas during peak primary production periods. This finding was also supported by our data from the 24-hour run, which showed a higher nighttime carbon flux in P. australis but (over a daily period) a much higher potential to fix carbon compared to native species and open water areas.
S o il R e s p ir a tio n 60
O pen N a tiv e P h ra g
-2
-1
Soil Respiration (mg C produced m hr )
50
40
b
b 30
a 20
a
a
10 a
0 0 3 -J u n -0 9
2 2 -J u n -0 9
1 5 - J u l- 0 9
0 6 -A u g -0 9
Figure 9. Soil respiration rates measured in the PVC collars over a 24-hour period.
M e th a n o g e n e s is
O pen N a tiv e P h ra g
300
-2
-1
Methanogensis (mg C produced m hr )
350
250
200
150
100
50
0 0 3 -J u n -0 9
2 2 -J u n -0 9
1 5 -J u l- 0 9
0 6 -A u g -0 8
Figure 10. Methanogenesis rates measured in the PVC collars over a 24-hour period. N e t E c o s y s te m E x c h a n g e o f C a r b o n 3000
2500
2000
-2
-1
NEE (mg C fixed m hr )
c
O pen N a t iv e P h ra g
1500
c
1000
b b 500
b a
a
a
a
0 0 4 -J u n -0 9
2 2 -J u n -0 9
1 5 - J u l- 0 9
0 6 -A u g -0 9
D a te
Figure 11. Net ecosystem exchange of carbon measured with the in-situ carbon dioxide flux chambers.
24 Hour NEE 800 Native Phragmites
-2
-1
NEE (mg C fixed m hr )
600
400
200
0
-200
-400 05:00:00
09:00:00
13:00:00
17:00:00
21:00:00
Time
Figure 12. Net ecosystem exchange of carbon measured with the in-situ carbon dioxide flux chambers over a 24-hour period.
Impact of Phragmites australis on the biogeochemistry of riverine wetlands in Nebraska Biogeochemical data from 3 riverine wetlands in Nebraska have been collected for fall 2008, spring 2009, and summer 2009. Sites included in this study range from heavily (Arapahoe) to moderately (Martin’s Reach) to sparsely (Bassway Pond) infested with P. australis. Data suggest that the impact of P. australis on carbon and nitrogen cycling was greatest in the heavily infested site and overall these cycles were enhanced beneath the invasive species compared to native species. Specifically, we observed higher organic matter concentrations underneath P. australis (Figure 13) despite labile carbon rates also being high in the Arapahoe site (Figure 14). This was most likely an artifact of the prolific aboveground biomass produced by P. australis compared to much smaller native species such as sedges and rush. Further, the higher labile carbon pool was supporting greater concentrations of microbial biomass (Figure 15) and this in turn was fueling higher rates of nitrogen cycling (Figures 16 and 17). Overall this project has found that the infestation of a wetland with P. australis results in more carbon sequestration and a greater microbial abundance which can cycle and remove nitrogen at higher rates. These findings are most likely due to the trapping of fine sediments in dense stands of P. australis. The fine materials contain more labile carbon which is bio-available to microbes and higher surface area for microbes to colonize. Thus the infestation of P. australis in riverine wetlands in Nebraska is enhancing biogeochemical processes but at the same time is irreparably altering sediment structure.
60
a
Phragmites Native
-1
Organic Matter (g kg )
50 40 b
30 20 10 0
Arapahoe
Bassway
Martin's Reach
Figure 13. Organic matter concentrations observed in the three study sites beneath Phragmites australis and native species (either sedge or rush). Data suggest that sediments beneath P. australis accumulate more carbon particularly at the heavily infested site (Arapahoe). 400 Phragmites Native
300
-1
-1
Labile Carbon (µg C g day )
a
200 b 100
0 Arapahoe
Bassway
Martin's Reach
Figure 14. Labile carbon rates obtained from sediments collected from the three study sites. At the heavily infested site (Arapahoe) sediments beneath Phragmites australis have greater rates of easily degradable carbon suggesting these sediments can support more abundant microbial communities.
2000 Phragmites Native
Microbial Biomass (µg C g-1)
a 1500
a
1000 b
b 500
0 Arapahoe
Bassway
Martin's Reach
Figure 15. Estimates of microbial biomass in sediments collected from the three study sites. In the two most infested sites, data suggest that microbial communities are most abundant beneath Phragmites australis compared to native species. 30 Phragmites Native
a
-1
-1
Nitrification (µg N g day )
25 20
a
a
15 b 10
b
5
b
0 Arapahoe
Bassway
Martin's Reach
Figure 16. Nitrification rates, a process that converts ammonia (toxic compound to aquatic biota) to nitrate, observed at the three study sites. Results show that rates are higher beneath Phragmites australis at all sites.
25
Denitrification (µg N g-1 day-1)
a
Phragmites Native
20 10
a
5 b
b 0 Arapahoe
Bassway
Martin's Reach
Figure 17. Denitrification rates, a process that removes nitrate from an ecosystem by converting it to nitrogen gas, observed at the three study sites. Results show that rates are higher beneath Phragmites australis at the two most infested sites.
Figure 1. Picture showing the helicopter spraying the Phragmites australis within the Arapahoe Wetland on July 22, 2009.
Figure 2. Picture of the helicopter spraying Phragmites australis along the banks of the South Channel of the Platte River on September 25, 2009. Evapotranspiration estimates using meteorological instruments Throughout the summer data has been collected and instruments checked periodically for any problems. As a result of shorter days, the temperature aspirators at the meteorological station in the Cattail have been turned off to conserve power. The large aperture scintillometer (LAS) and the station in the P. australis will continue to run until the beginning of November to get the longest data set possible before the LAS and the station aspirators need to be shut down. The wetland was also mapped with a differential GPS (DGPS), which was measured with sub meter accuracy (Figure 3). Precise measurements were needed to establish an exact distance between the LAS receiver and transmitter to derive sensible heat flux. As the growing season is wrapping up, the data is being analyzed for quality control. Except for a couple of weeks in March/April when a station failed due to insufficient power, we received full data throughout the growing season (Figure 4). We found that the upper temperature sensor at the P. australis site (Bowen 1) was reading erroneous data from June 13th – July 23rd (Figure 5). Since this measurement is used for the Bowen ratio energy balance and the calculation of sensible heat flux from the LAS, it is important to fill in the data gaps with the least amount of error possible. We are also in the process of determining how sensitive the LAS setup is to the inputs of plant height, receiver/transmitter distance, water level, temperature, and relative humidity. Preliminary results have shown that the LAS setup is most affected by plant height. This will help determine how long each time step should be and the statistical error between each derivation of sensible heat flux. Finally we have estimated the Cattail and P. australis plant height throughout the beginning of the growing season (Figure 6). This will help determine the plant height when sensible heat is calculated and also give an illustration of how the two plants have grown with respect of each other.
Figure 3. Aerial image of the wetland overlaid with points taking from a DGPS unit. The yellow circles represent the wetland boundary, the red triangles represent the LAS transmitter (western) and receiver (eastern), and the purple circles are Bowen 1 (western) and Bowen 2 (eastern). The yellow circles that cut across the wetland are the approximate location were the Phragmites australis transition to cattail as you move west to east.
Figure 4. The daily average albedo over Phragmites australis at Bowen 1 and Cattail at Bowen 2. Albedo uses the measurements of incoming shortwave and net shortwave for both stations. This is a good illustration of all the data collected throughout the year.
Figure 5. The average daily upper temperature difference between Bowen 1 (Phragmites australis) and Bowen 2 (Cattail). The period when the difference becomes large is the time when the upper sensor was reading erroneous data.
Figure 6. Estimated plant heights of Phragmites australis and Cattail.
The use of groundwater fluctuations to estimate evapotranspiration The interaction between shallow groundwater and land surface processes (e.g., actual evapotranspiration-ETa) through the mechanisms of capillary rise and groundwater evapotranspiration (ETg) may play an important role in the ecohydrological system, particularly in semi-arid regions with limited water availability. ETg mainly depends upon the depth of groundwater table, soil texture, atmospheric driving power, and surface vegetation cover. In order to quantify the effect of groundwater on ETa in regions with shallow water tables, we modeled evapotranspiration under different depths of groundwater tables, soil textures, and surface cover conditions. To simulate the groundwater influence on ET in the Republican River basin, we chose a HPRCC observation station near Champion, NE to calculate potential ET using the Penman-
Monteith equation under reference ET and bare soil ET conditions for 28 years (1982-2008; Figure 7). A process-based hydrodynamic model, Hydrus-1D, is used in this study (Simunek et al., 2005) which is based on the Richards equation for solving soil moisture flow in porous media. The constant head lower boundary condition is used to represent the groundwater table. The simulation results are plotted in Figure 8. In general, groundwater has a significant impact on surface evapotranspiration. The degree of the impact decreases almost exponentially with increasing water depths. Furthermore, coarser soils tend to have less impact on ETa at the same depth of water table (Figure 8).
Figure 7. Reference ET and potential bare soil ET in Champion station.
Figure 8. Percentage of groundwater contribution on ET for different soil textures, surface covers and groundwater table depths.
Carbon dynamics in an invaded riparian wetland in South-Central Nebraska The field season for 2009 was completed during the first week of October. Since the last quarterly report, 3 more field days have completed as well as a 24-hour run. The following figures represent preliminary results from the study and bars with different letters are statistically different (α = 0.05). Soil respiration was low relative to the other components of the carbon balance with significant differences early in the season (Figure 9) while methanogenesis rates were roughly five times higher than soil respiration rates with similar rates between all three habitat types (Figure 10). NEECarbon was highest in P. australis areas and displayed strong seasonality peaking during late June (Figure 11). NEE of carbon also displayed strong diurnal variation peaking in mid-afternoon; diurnal swings were greatest in P. australis (Figure 12). Although sampling in the field has been completed, all of the data has not been analyzed. We expect to finish laboratory analysis in the coming weeks and final conclusions will be made shortly thereafter. Soil respiration rates were highest in the P. australis areas early in the season, but overall soil respiration does not appear to be a major source of carbon in this environment. On the other hand, methanogenesis was similar between all three habitat types and appears to be the major source of carbon compared to other studies conducted in natural wetlands. This has significant implications, as methane has a global warming potential that is 20 times higher than carbon dioxide. NEECarbon showed significant differences through the first three sampling dates, with P. australis fixing 2-5 times more carbon than open water and native areas during peak primary production periods. This finding was also supported by our data from the 24-hour run, which showed a higher nighttime carbon flux in P. australis but (over a daily period) a much higher potential to fix carbon compared to native species and open water areas.
S o il R e s p ir a tio n 60
O pen N a tiv e P h ra g
-2
-1
Soil Respiration (mg C produced m hr )
50
40
b
b 30
a 20
a
a
10 a
0 0 3 -J u n -0 9
2 2 -J u n -0 9
1 5 - J u l- 0 9
0 6 -A u g -0 9
Figure 9. Soil respiration rates measured in the PVC collars over a 24-hour period.
M e th a n o g e n e s is
O pen N a tiv e P h ra g
300
-2
-1
Methanogensis (mg C produced m hr )
350
250
200
150
100
50
0 0 3 -J u n -0 9
2 2 -J u n -0 9
1 5 -J u l- 0 9
0 6 -A u g -0 8
Figure 10. Methanogenesis rates measured in the PVC collars over a 24-hour period. N e t E c o s y s te m E x c h a n g e o f C a r b o n 3000
2500
2000
-2
-1
NEE (mg C fixed m hr )
c
O pen N a t iv e P h ra g
1500
c
1000
b b 500
b a
a
a
a
0 0 4 -J u n -0 9
2 2 -J u n -0 9
1 5 - J u l- 0 9
0 6 -A u g -0 9
D a te
Figure 11. Net ecosystem exchange of carbon measured with the in-situ carbon dioxide flux chambers.
24 Hour NEE 800 Native Phragmites
-2
-1
NEE (mg C fixed m hr )
600
400
200
0
-200
-400 05:00:00
09:00:00
13:00:00
17:00:00
21:00:00
Time
Figure 12. Net ecosystem exchange of carbon measured with the in-situ carbon dioxide flux chambers over a 24-hour period.
Impact of Phragmites australis on the biogeochemistry of riverine wetlands in Nebraska Biogeochemical data from 3 riverine wetlands in Nebraska have been collected for fall 2008, spring 2009, and summer 2009. Sites included in this study range from heavily (Arapahoe) to moderately (Martin’s Reach) to sparsely (Bassway Pond) infested with P. australis. Data suggest that the impact of P. australis on carbon and nitrogen cycling was greatest in the heavily infested site and overall these cycles were enhanced beneath the invasive species compared to native species. Specifically, we observed higher organic matter concentrations underneath P. australis (Figure 13) despite labile carbon rates also being high in the Arapahoe site (Figure 14). This was most likely an artifact of the prolific aboveground biomass produced by P. australis compared to much smaller native species such as sedges and rush. Further, the higher labile carbon pool was supporting greater concentrations of microbial biomass (Figure 15) and this in turn was fueling higher rates of nitrogen cycling (Figures 16 and 17). Overall this project has found that the infestation of a wetland with P. australis results in more carbon sequestration and a greater microbial abundance which can cycle and remove nitrogen at higher rates. These findings are most likely due to the trapping of fine sediments in dense stands of P. australis. The fine materials contain more labile carbon which is bio-available to microbes and higher surface area for microbes to colonize. Thus the infestation of P. australis in riverine wetlands in Nebraska is enhancing biogeochemical processes but at the same time is irreparably altering sediment structure.
60
a
Phragmites Native
-1
Organic Matter (g kg )
50 40 b
30 20 10 0
Arapahoe
Bassway
Martin's Reach
Figure 13. Organic matter concentrations observed in the three study sites beneath Phragmites australis and native species (either sedge or rush). Data suggest that sediments beneath P. australis accumulate more carbon particularly at the heavily infested site (Arapahoe). 400 Phragmites Native
300
-1
-1
Labile Carbon (µg C g day )
a
200 b 100
0 Arapahoe
Bassway
Martin's Reach
Figure 14. Labile carbon rates obtained from sediments collected from the three study sites. At the heavily infested site (Arapahoe) sediments beneath Phragmites australis have greater rates of easily degradable carbon suggesting these sediments can support more abundant microbial communities.
2000 Phragmites Native
Microbial Biomass (µg C g-1)
a 1500
a
1000 b
b 500
0 Arapahoe
Bassway
Martin's Reach
Figure 15. Estimates of microbial biomass in sediments collected from the three study sites. In the two most infested sites, data suggest that microbial communities are most abundant beneath Phragmites australis compared to native species. 30 Phragmites Native
a
-1
-1
Nitrification (µg N g day )
25 20
a
a
15 b 10
b
5
b
0 Arapahoe
Bassway
Martin's Reach
Figure 16. Nitrification rates, a process that converts ammonia (toxic compound to aquatic biota) to nitrate, observed at the three study sites. Results show that rates are higher beneath Phragmites australis at all sites.
25
Denitrification (µg N g-1 day-1)
a
Phragmites Native
20 10
a
5 b
b 0 Arapahoe
Bassway
Martin's Reach
Figure 17. Denitrification rates, a process that removes nitrate from an ecosystem by converting it to nitrogen gas, observed at the three study sites. Results show that rates are higher beneath Phragmites australis at the two most infested sites.
