Chris C. Tanner

Plants for constructed wetland treatment systems — A comparison of the growth and nutrient uptake of eight emergent species

Abstract Allocation of above and below-ground growth and nutrient uptake, and pollutant removal were compared for Schoenoplectus validus, Phragmites australis, Glyceria maxima, Baumea articulata, Bolboschoenus fluviatilis, Cyperus involucratus, Juncus effusus and Zizania latifolia. Plants were grown in triplicate 0.238 m2 × 0.6 m deep gravel-bed wetland mosocosms fed with dairy farm wastewaters pre-treated in an anaerobic lagoon. After 124 days, mean species total biomass ranged from 0.3 to 7.4 kg m−2, with above-below-ground ratios between 0.35 and 3.35. Growth of Baumea and Juncus was relatively poor. Zizania and Glyceria showed the highest above-ground biomass values, ranging between 3 and 4 kg m−2. Above-ground tissue concentrations of nitrogen (N) and phosphorus (P) ranged from 15 to 32 and 1.3 to 3.4 mg g−1, respectively. Maximum plant accumulations of 135 g N m−2 and 18.5 g P m−2 accounted for around 30% of the levels supplied in wastewaters. Mean removals of 76–88% of suspended solids, 77–91% of biochemical oxygen demand, and 79–93% of total P were recorded for the established mesocosms irrespective of plant species. Mean removal of total N ranged from 65 to 92%, showing a significant positive linear correlation with plant biomass. Comparisons are made with information from other studies on establishment rate, productivity, nutrient uptake, potential for root-zone aeration and general life history traits in constructed wetlands.

Ammonium removal from wastewaters using natural New Zealand zeolites

Abstract Ammoniacal nitrogen (ammonia and ammonium) in agricultural wastewaters can promote eutrophication of receiving waters and be potentially toxic to fish and other aquatic life. Zeolites, which are hydrated aluminum‐silicate minerals, have an affinity for ammonium ions (NH4 +) and are, therefore, potentially useful in removing this contaminant from wastewaters. The major objectives of this study were to evaluate the capacity of two natural New Zealand zeolites (clinoptilolite and mordenite) to remove NH4 + from a range of wastewaters under both batch and flow‐through conditions. Effects of two zeolite particle size ranges (0.25–0.50 mm and 2.0–2.83 mm) on NH4 + removal performance were also investigated. Results obtained from the batch adsorption experiments indicated that both zeolites tested, regardless of their particle sizes, were equally effective (87–98%) at NH4 + removal from domestic wastewaters or synthetic solutions containing NH4 + concentrations of up to 150 gNH4‐N m−3. However, mordenit...

Effect of water level fluctuation on nitrogen removal from constructed wetland mesocosms

Nitrogen removal processes were investigated at three frequencies of water level fluctuation, static, low and high (0, 2 and 6 d−1), in duplicate gravel-bed constructed wetland mesocosms (0.145 m3) with and without plants (Schoenoplectus tabernaemontani). Fluctuation was achieved by temporarily pumping wastewater into a separate tank (total drain time ∼35 min). Intensive sampling of the mesocosms, batch-fed weekly with ammonium-rich (∼100 g m−3 NH4-N) farm dairy wastewaters, showed rates of chemical oxygen demand (COD) and total Kjeldahl nitrogen (TKN) removal increased markedly with fluctuation frequency and in the presence of plants. Nearly complete removal of NH4-N was recorded over the 7 day batch period at the highest level of fluctuation, with minimal enhancement by plants. Redox potentials (Eh) at 100 mm depth rose from initial levels of around −100 to >350 mV and oxidised forms of N (NO2 and NO3) increased to ∼40 g m−3, suggesting conditions were conducive to microbial nitrification at this level of fluctuation. In the unplanted mesocosms with low or zero fluctuation, mean NH4-N removals were only 28 and 10%, respectively, and redox potentials in the media remained low for a substantial part of the batch periods (mid-batch Eh ∼+100 and −100 mV, respectively). In the presence of wetland plants, mean NH4-N removal in the mesocosms with low or zero fluctuation rose to 71 and 54%, respectively, and COD removal (>70%) and redox potential (mid-batch Eh>200 mV) were markedly higher than in the unplanted mesocosms. Negligible increases in oxidised N were recorded at these fluctuation frequencies, but total nitrogen levels declined at mean rates of 2.4 and 1.8 g m−2 d−1, respectively. NH4-N removal from the bulk water in the mesocosms was well described (R2=0.97–0.99) by a sorption-plant uptake-microbial model. First-order volumetric removal rate constants (kv) rose with increasing fluctuation frequency from 0.026 to 0.46 d−1 without plants and from 0.042 to 0.62 d−1 with plants. As fluctuation frequency increased, reversible sorption of NH4-N to the media, and associated biofilms and organic matter, became an increasingly important moderator of bulk water concentrations during the batch periods. TN mass balances for the full batch periods suggested that measured plant uptake estimates of between 0.52 and 1.07 g N m−2 d−1 (inversely related to fluctuation frequency) could fully account for the increased overall removal of TN recorded in the planted systems. By difference, microbial nitrification-denitrification losses were therefore estimated to be approximately doubled by low-level fluctuation from 0.7 to 1.4 g N m−2 d−1 (both with and without plants), rising to a maximum rate of 2.1 g N m−2 d−1 at high fluctuation, in the absence of competitive uptake by plants.

Seasonality of macrophytes and interaction with flow in a New Zealand lowland stream

Introduced submerged macrophytes have come to dominate many shallow water bodies in New Zealand, and are a common component of many lowland streams. We investigated the seasonal variation of macrophyte abundance, its influence on flow and channel volume, and the implications of this on stream habitat and functioning in Whakapipi Stream, a typical lowland stream draining a predominantly agricultural catchment.Abundance of macrophytes over the summer was primarily controlled by the phenological cycles of the two dominant species. Mean minimum total macrophyte biomass (36 g m−2) and cover (7%) occurred in winter (June and August, respectively), and mean maximum biomass (324 g m−2), and cover (79%) occurred in late summer (March and February respectively). Egeria densa comprised the majority of both cover and biomass during the study period, except early summer (December) when Potamogeton crispus was prevalent in the shallow stream reaches.Macrophyte beds had a major impact on summer stream velocities, reducing average velocities by an estimated 41%. Stream cross-sectional area was maintained at relatively stable levels similar to that recorded over winter, when stream discharge was in the order of seven times greater. The mean velocity distribution coefficient (α), and Mannings roughness coefficient (n) were dependent on and displayed a positive linear relationship with macrophyte abundance. The velocity distribution coefficient is recommended as a better indicator of macrophyte effects on velocity in natural streams, as it does not assume uniform velocity, channel depth and slope within the stream reach.Our study shows that submerged macrophytes play an important structuring role within the stream during the summer period, where macrophyte beds act as semi-permeable dams, retarding flow velocities and increasing stream depth and cross-sectional area. This promotes habitat heterogeneity by creating a greater range of flow velocity variation, and also provides large stable low-flow areas. Other likely ecosystem effects resulting from macrophyte/velocity interactions include increased sedimentation, potential for nutrient processing and increased primary production, both by macrophytes and attached epiphyton. The complex architecture of submerged macrophytes and their influence on stream flow may also provide an increased diversity of habitat for other aquatic biota. We propose that management of degraded lowland streams such as the Whakapipi Stream to maintain stretches with moderate quantities of submerged macrophytes interspersed with shaded areas would optimise stream health during low summer flows.

Modelling biofilm nitrogen transformations in constructed wetland mesocosms with fluctuating water levels

A mathematical model has been developed that attempts to reproduce patterns of nitrogen removal observed in experiments investigating constructed wetland treatment of ammonium-rich wastewaters under a range of frequencies of water level fluctuation. The experiments were carried out using batch-fed gravel-filled mesocosms, with and without plants, subjected to fluctuating oxygen input through a drain-and-refill regime. Experimental data showed that removal of ammoniacal-nitrogen (NH4–N) and chemical oxygen demand (COD) increased markedly with fluctuation frequency. Plants also tended to enhance the removal of NH4-N and COD. For the highest fluctuation frequency (16 cycles per day, plants absent), accumulation of oxidised nitrogen (NOx–N) was observed to continue even when the wastewater NH4–N had disappeared from solution. A process-based numerical model was developed to elucidate the strength of competing nitrogen transformation processes, which were postulated to be strongly influenced by biofilms and adsorption/desorption associated with gravel surfaces and organic matter, particularly when the mesocosm was empty and liquid on the biofilms was exposed to the atmosphere. A combination of thin-biofilm theory, the microbiological kinetics in the IAWQ activated sludge model No. 2, reversible sorption kinetics and mixing equations was used to demonstrate that very rapid initial decreases in NH4–N were likely to be caused by adsorption onto the gravel and that during the latter part of the batch periods nitrification was likely to be controlled by the rate of desorption of this NH4–N. Nitrification could therefore continue when NH4–N was almost absent from the bulk water. At moderate-to-high fluctuation frequencies (≥6 cycles per day) the presence of plants enhanced NH4–N removal and NOx–N accumulation, through a combination of direct uptake of NH4–N and increased root-zone reaeration.

Substrate and filter materials to enhance phosphorus removal in constructed wetlands treating diffuse farm runoff: a review

Abstract Constructed and restored wetlands have significant potential to reduce nutrient losses in drainage waters from New Zealand farms. While both types of wetland show reasonably good nitrogen (N) removal efficiencies, they are not always so effective at phosphorus (P) removal and their flooded topsoils can be net sources of P. Wetland P-removal efficiency could be enhanced, either by adding a P-retentive amendment to the soil in the bottom of the wetland or installing a porous filter with a high P adsorbency and retention capacity at the end of the wetland. This review was carried out to evaluate a range of materials reported in the scientific literature as having the ability to remove P from water. Materials reviewed include: naturally occurring materials, such as soils, sands, clays and aggregates; processed and modified materials; and waste materials. The reported performance of the materials reviewed varied widely. A simple scoring system based on P-removal characteristics, availability, likely cost and potential reuse or disposal on saturation was used to identify the materials with most promise as soil amendments or filters for constructed wetlands. Allophane, Papakai tephra, limestone and alum were judged as materials with the most potential as soil amendments, while limestone, slag, seashells, shell-sand and tree bark had most potential as filter materials. Another possible approach is to use subsoil or a mix of subsoil and topsoil as the growth media in the base of the wetland to avoid P release on flooding of P-rich agricultural topsoils.

Algal abundance, organic matter, and physico‐chemical characteristics of dairy farm facultative ponds: Implications for treatment performance

Abstract Six Waikato (New Zealand) dairy farm facultative ponds (DFPs), which met the larger sizes specified in recent dairy industry guidelines, were sampled monthly over an annual period. Median wastewater BOD5 was 65 g m‐3, suspended solids (SS) 206 g m‐3, ammoniacal N 37 g m‐3, total nitrogen 69 g m‐3, and faecal coliforms 24 000 (100 ml)‐1. This was 20–70% better than reported for DFPs built to previous guidelines, except for SS levels which were within reported ranges. However, performance was highly variable and only ½ of the DFPs studied consistently met an effluent standard of ≤ 100 g m‐3 BOD 5 and only one reached ≤ 150 g m‐3 SS. Removal of BOD 5 was much lower than recorded for SFPs in New Zealand with equivalent BOD 5 loading. Although the mean euphotic depth was only 0.11 m, algal biomass in DFPs was similar to that recorded for SFPs. Low phaeophytin concentrations and daytime oxygen exceeding 200% saturation in the shallow epilimnion on sunny days suggested a relatively healthy photosynthetic algal population was present in the DFPs. However, wastewater entering DFPs showed high median COD levels (1420 g m‐2). COD:BOD 5 ratios of c. 12.1 (compared with 1.5–1.8 for SFPs) and BOD 10 :BOD 5 ratios of c. 2 indicated the presence of a large pool of slowly degradable organic matter in the wastewater. This resulted in sustained exertion of BOD in the pond, explaining the “apparent” poor removal of BOD 5 by DFPs. Conductivity was found to be a useful single‐measure indicator of overall pond performance and management of sludge levels in the preceding anaerobic pond was identified as a key factor affecting DFP performance. Further improvements in dairy farm stabilisation pond performance are likely to be required on many farms to meet receiving water guidelines for the protection of water quality and aquatic life.

Floating Treatment Wetland influences on the fate of metals in road runoff retention ponds.

A field trial comparing the fate of metals in two parallel stormwater retention ponds, one of which was retrofitted with a Floating Treatment Wetland (FTW), was carried out near Auckland, New Zealand. Results suggest that the FTW increased metal accumulation in the pond sediment especially in summer due to lower sediment Eh, more anoxic water column, neutral pH and greater source of organic matter (OM) induced by the FTW. These factors combined with higher temperature enhanced metal sorption onto OM, flocculation of particulate pollutants, metal sulphide formation and reduced OM degradation and thus limited release of metals. Unlike Zn, Cu speciation in the pond sediment was relatively unchanged under various sediment Eh conditions due to its strong binding property with sulphide and OM. Occasional moderate metal release was detected from the FTW pond sediment likely due to aerobic OM degradation at the beginning of spring and/or hydroxides reduction when sediments became reduced later in the season. No release was noticed from the conventional pond sediment likely due to biosorption and/or uptake by algae which developed in the conventional pond and settled on the bottom sediment. Direct uptake by the plants of the FTW and sorption onto root plaques are not thought to be significant removal pathways. Nevertheless roots play a major role in trapping particulate pollutants, eventually sloughing off to settle on the bottom of the pond, and provide an adequate substrate for bacterial development due to release of organic compounds which are both essential for dissolved metal sorption and metal sulphide formation.

Effects of suspended solids on the establishment and growth of Egeria densa

Abstract To identify levels of suspended solids (SS) in Lake Waahi (Huntly, New Zealand) favourable for the re-establishment of Egeria densa Planchon, shoots were grown in 2 m deep tanks filled with water transported from the lake and maintained at selected SS loadings between 5 and 40 g m −3 (predominantly compromised kaolinitic clays). Plant growth was measured over periods of 44–47 days in spring, summer and autumn. Highest relative growth rates (RGR) were recorded in summer (maximum 40 mg g −1 day tt-1 ). Egeria propagules growing from a depth of 1.85 m showed positive growth responses at SS levels up to approximately 25 g m −3 ( K d ≈ 1.75) in spring and autumn, and approximately 35 g m −3 ( K d ≈ 1.95) in summer. At SS levels up to 15 g m −3 ( K d = 1.5 m −1 ), growth was little affected during summer, while during spring and autumn biomass accumulation was reduced to about 60% and RGR values to about 70% of the maximum seasonal values recorded. Egeria shoots showed maximum elongation at about 10–20 g m −3 SS ( K d = 1.3−1.65). Plant architecture became less branched with increasing SS and the number of roots produced decreased. Implications for the establishment of Egeria in turbid waters are discussed.

Stormwater nitrogen removal performance of a floating treatment wetland.

The nitrogen (N) removal efficiency and effluent quality of two parallel stormwater retention ponds, one retrofitted with a floating treatment wetland (FTW) and one without any vegetation, was compared in a field trial. This study shows that inclusion of FTWs in stormwater retention ponds has potential to moderately improve N removal. Median FTW outlet event mean concentrations (EMCs) were lower than median inlet and control pond outlet EMCs for all species of N, except for NH(4)-N. Performance was statistically better from late spring to end autumn due to higher organic nitrogen (ON) removal and denitrification in presence of the FTW. Low dissolved oxygen (DO), higher temperature and increased organic matter (OM) and microbial activity below the FTW, likely facilitated the higher denitrification rates observed over this period. Greater sediment N accumulation in the FTW pond also contributed to its higher overall N removal. Higher OM availability in the FTW pond due to release of root exudates and supply of detritus from plant die-back may have contributed to floc formation in the water column, increasing particulate ON settlement. Enhanced ON mineralisation may also be responsible but was probably limited in summer due to the low DO induced by the FTW. Direct uptake by the plants appears to be of less importance.