title: A comparison of different approaches for measuring denitrification rates in a nitrate removing bioreactor

authors: Warneke, Sören

subjects: Denitrification

abstract: Denitrifying woodchip bioreactors (denitrification beds) are increasingly used to remove excess nitrate (NO₃⁻) from point-sources such as wastewater effluent or subsurface drains from agricultural fields. NO₃⁻ removal in these beds is assumed to be due to microbial denitrification but direct measurements of denitrification are lacking. Our objective was to test four different approaches for measuring denitrification rates in a denitrification bed that treated effluent discharged from a glasshouse. We compared these denitrification rates with the rate of NO₃⁻ removal along the length of the bed. The NO₃⁻ removal rate was 8.73 ± 1.45 g m⁻³ d⁻¹. In vitro acetylene inhibition assays resulted in highly variable denitrification rates (DRAI) along the length of the bed and generally 5 times greater than the measured (NO₃⁻- N removal rate. An in situ push–pull test, where enriched ¹⁵N- NO₃⁻was injected into 2 locations along the bed, resulted in rates of 23.2 ± 1.43 g N m⁻³ d⁻¹ and 8.06 ± 1.64 g N m⁻³ d⁻¹. The denitrification rate calculated from the increase in dissolved N2 and N2O concentrations (DRN2) along the length of the denitrification bed was 6.7 ± 1.61 g N m⁻³ d⁻¹. Lastly, denitrification rates calculated from changes in natural abundance measurements of δ¹⁵N-N₂ and δ¹⁵N- NO₃⁻ along the length of the bed yielded a denitrification rate (DRNA) of 6.39 ± 2.07 g m⁻³ d⁻¹. Based on our experience, DRN2 measurements were the easiest and most efficient approach for determining the denitrification rate and N₂O production of a denitrification bed. However, the other approaches were useful for testing other hypotheses such as factors limiting denitrification or may be applied to determine denitrification rates in environmental systems different to our study site. DRN2 does require very careful sampling to avoid atmospheric N2 contamination but could be used to rapidly determine denitrification rates in a variety of aquatic systems with high N2 production and even water flows. These measurements demonstrated that the majority of NO₃⁻ removal was due to heterotrophic denitrification.

text: A comparison of different approaches for measuring denitrification rates in a nitrate removing bioreactor Denitrifying woodchip bioreactors (denitrification beds) are increasingly used to remove excess nitrate (NO₃⁻) from point-sources such as wastewater effluent or subsurface drains from agricultural fields. NO₃⁻ removal in these beds is assumed to be due to microbial denitrification but direct measurements of denitrification are lacking. Our objective was to test four different approaches for measuring denitrification rates in a denitrification bed that treated effluent discharged from a glasshouse. We compared these denitrification rates with the rate of NO₃⁻ removal along the length of the bed. The NO₃⁻ removal rate was 8.73 ± 1.45 g m⁻³ d⁻¹. In vitro acetylene inhibition assays resulted in highly variable denitrification rates (DRAI) along the length of the bed and generally 5 times greater than the measured (NO₃⁻- N removal rate. An in situ push–pull test, where enriched ¹⁵N- NO₃⁻was injected into 2 locations along the bed, resulted in rates of 23.2 ± 1.43 g N m⁻³ d⁻¹ and 8.06 ± 1.64 g N m⁻³ d⁻¹. The denitrification rate calculated from the increase in dissolved N2 and N2O concentrations (DRN2) along the length of the denitrification bed was 6.7 ± 1.61 g N m⁻³ d⁻¹. Lastly, denitrification rates calculated from changes in natural abundance measurements of δ¹⁵N-N₂ and δ¹⁵N- NO₃⁻ along the length of the bed yielded a denitrification rate (DRNA) of 6.39 ± 2.07 g m⁻³ d⁻¹. Based on our experience, DRN2 measurements were the easiest and most efficient approach for determining the denitrification rate and N₂O production of a denitrification bed. However, the other approaches were useful for testing other hypotheses such as factors limiting denitrification or may be applied to determine denitrification rates in environmental systems different to our study site. DRN2 does require very careful sampling to avoid atmospheric N2 contamination but could be used to rapidly determine denitrification rates in a variety of aquatic systems with high N2 production and even water flows. These measurements demonstrated that the majority of NO₃⁻ removal was due to heterotrophic denitrification.

year: 2011

title: Reply to Mahowald and Gibson and to Heggarty: No problems with short words, and no evidence provided

authors: Pagel, Mark

abstract: Mahowald and Gibson (1) suggest that the shorter word length of frequently used words, and not their stability, could mean that chance sound correspondences account for the pattern of results we report for cognate relationships among proto-words in our study of seven Eurasian language families (2). However, their −0.24 correlation between the phonological length of contemporary English words and our measure of cognate class size is not relevant to the question of chance sound correspondences among the proto-words from different language families. What must be demonstrated is that shorter proto-words were more likely to be judged cognate simply on the basis of their length.

text: Reply to Mahowald and Gibson and to Heggarty: No problems with short words, and no evidence provided Mahowald and Gibson (1) suggest that the shorter word length of frequently used words, and not their stability, could mean that chance sound correspondences account for the pattern of results we report for cognate relationships among proto-words in our study of seven Eurasian language families (2). However, their −0.24 correlation between the phonological length of contemporary English words and our measure of cognate class size is not relevant to the question of chance sound correspondences among the proto-words from different language families. What must be demonstrated is that shorter proto-words were more likely to be judged cognate simply on the basis of their length.

year: 2013

title: Boat electrofishing salvage of fish in the Lower Mangamahoe Dam reservoir

authors: Hicks, Brendan J.

abstract: The aim of the survey was to salvage fish from the Lower Mangamahoe Dam reservoir before dewatering and dam removal. We used the University of Waikato’s 4.5 m-long, aluminium-hulled electrofishing boat to catch a total of 140 fish weighing an estimated 37.0 kg along 8 fishing tracks sites on 24 February 2022. These tracks comprised 2,807 lineal m and 11,228 m2 in area. Shortfin eels (Anguilla australis) and common bullies (Gobiomorphus cotidianus) were the only fish species present. Mean density of eels caught was 2.9 fish 100 m–2 and mean biomass was 7.84 g m–2. The eels and bullies were transferred to sites downstream in the Waiwhakaiho River by iwi members of the two hapū - Ngāti Te Whiti and Ngāti Tawhirikura. Water clarity, expressed as black disc distance (BDD, 1.05 m), was good for a shallow lake, and water temperature and water conductivity were close to optimum for electrofishing. Poor water clarity can reduce the efficiency of electrofishing, so we left time after fishing each track for the sediment suspended by the propellor wash to sink before refishing a track.

text: Boat electrofishing salvage of fish in the Lower Mangamahoe Dam reservoir The aim of the survey was to salvage fish from the Lower Mangamahoe Dam reservoir before dewatering and dam removal. We used the University of Waikato’s 4.5 m-long, aluminium-hulled electrofishing boat to catch a total of 140 fish weighing an estimated 37.0 kg along 8 fishing tracks sites on 24 February 2022. These tracks comprised 2,807 lineal m and 11,228 m2 in area. Shortfin eels (Anguilla australis) and common bullies (Gobiomorphus cotidianus) were the only fish species present. Mean density of eels caught was 2.9 fish 100 m–2 and mean biomass was 7.84 g m–2. The eels and bullies were transferred to sites downstream in the Waiwhakaiho River by iwi members of the two hapū - Ngāti Te Whiti and Ngāti Tawhirikura. Water clarity, expressed as black disc distance (BDD, 1.05 m), was good for a shallow lake, and water temperature and water conductivity were close to optimum for electrofishing. Poor water clarity can reduce the efficiency of electrofishing, so we left time after fishing each track for the sediment suspended by the propellor wash to sink before refishing a track.

year: 2022