Native Forest Catchments Research Articles

The effect of the ‘Las Maquinas’ wildfire of 2017 on the hydrologic balance of a high conservation value Hualo (Nothofagus glauca (Phil.) Krasser) forest in central Chile

The large wildfires of January 2017 burned more than 500,000 ha, including areas of high conservation value native forest, in central Chile. Runoff, streamflow and water balance were measured in a native forest catchment for 7 years before and 2 years after the fires. The annual peak flows and runoff coefficients decreased after the fire as did summer flows and total streamflow. These reductions in flow were despite rainfall being higher in the two years after the fire than in the two years before the fire. The forest re-sprouted vigorously after the fire and evapotranspiration in the second year after the fire was approximately two thirds of the rate before the fire. While the forest water use is recovering rapidly, streamflow in the two years after the fire was reduced relative to the seven years before the fire. In the two years after the fires, more than 50% of rainfall is not accounted for by either evapotranspiration or by streamflow. Potential explanations for this gap in the water balance include recovery in storage after the fire and increased bypass flow below the measuring weirs.

Connecting through space and time: catchment-scale distributions of bacteria in soil, stream water and sediment.

Terrestrial and aquatic environments are linked through hydrological networks that transport abiotic components from upslope environments into aquatic ecosystems. However, our understanding of how bacteria are transported through these same networks is limited. Here, we applied 16S rRNA gene sequencing to over 500 soil, stream water and stream sediment samples collected within a native forest catchment to determine the extent to which bacterial communities in these habitats are connected. We provide evidence that while the bacterial communities in each habitat were significantly distinct from one another (PERMANOVA pairwise P < 0.001), the bacterial communities in soil and stream samples were weakly connected to each other when stream sediment sample locations were downhill of surface runoff flow paths. This pattern decreased with increasing distance between the soil and sediment samples. The connectivity between soil and stream water samples was less apparent and extremely transient; the greatest similarity between bacterial communities in soil and stream water overall was when comparing stream samples collected 1 week post soil sampling. This study shows how bacterial communities in soil, stream water and stream sediments are connected at small spatial scales and provides rare insights into the temporal dynamics of terrestrial and aquatic bacterial community connectivity.

Following Rapoport's Rule: the geographic range and genome size of bacterial taxa decline at warmer latitudes.

We sought to test whether stream bacterial communities conform to Rapoport's Rule, a pattern commonly observed for plants and animals whereby taxa exhibit decreased latitudinal range sizes closer to the equator. Using a DNA sequencing approach, we explored the biogeography of biofilm bacterial communities in 204 streams across a ∼1000 km latitudinal gradient. The range sizes of bacterial taxa were strongly correlated with latitude, decreasing closer to the equator, which coincided with a greater than fivefold increase in bacterial taxonomic richness. The relative richness and range size of bacteria were associated with spatially correlated variation in temperature and rainfall. These patterns were observed despite enormous variability in catchment environmental characteristics. Similar results were obtained when restricting the same analyses to native forest catchments, thereby controlling for spatial biases in land use. We analysed genomic data from ∼500 taxa detected in this study, for which data were available and found that bacterial communities at cooler latitudes also tended to possess greater potential metabolic potential. Collectively, these data provide the first evidence of latitudinal variation in the range size distributions of freshwater bacteria, a trend which may be determined, in part, by a trade-off between bacterial genome size and local variation in climatic conditions.

Wood decay rates and macroinvertebrate community structure along contrasting human pressure gradients (Waikato, New Zealand)

Mass loss rates of wooden sticks (Betula platyphylla Sukaczev) and macroinvertebrate community composition were measured in the Waikato Region of northern New Zealand at 53 running water sites draining native forest catchments (reference), or characterised by urban, industrial, agroforestry or hydrological stressors. Overall wood substrates retained 80% of initial dry mass over 2–3 month incubation periods, equating to average daily decay coefficients (kd) of 0.0027 or 0.0002 when adjusted for degree days (kdd). There were no statistically significant differences in decay rates between stressor types and native forest reference sites. In contrast, macroinvertebrate richness and compositional metrics varied significantly from reference conditions for several stressor types. Wood decay rates were weakly related to macroinvertebrate community composition, while kdd was weakly but significantly related to % ‘worms’, %EPT* abundance and Quantitative Macroinvertebrate Community Index. The results indicate weak correspondence between macroinvertebrate indicators and wood decay rates, with spatial and temporal factors potentially masking stressor responses. Before wood decay can be widely used as an indicator of lotic ecosystem health there needs to be an improved understanding of environmental factors affecting breakdown rates.

Effects of riparian manipulation on stream communities in small streams: Two case studies

The effects of riparian manipulation in New Zealand are described for two case studies, one a short‐term study of the effects of the removal of riparian vegetation on fish, and the second, a long‐term study of the effect of re‐establishment of riparian vegetation on fish and benthic macro invertebrates. The first case study was an experiment carried out between November 2001 and May 2002. Overhanging bank vegetation and in‐stream wood were removed from short reaches of a small pastoral stream that had intact riparian margins, resulting in a change in stream structure with the formation of shallow uniform runs rather than pool and riffle structures as in unmodified reaches. The removal of bank cover and consequential instream habitat changes reduced inanga (Galaxias maculatus) densities by a factor of four within months of vegetation removal, showing the importance of instream cover and habitat to inanga. Adult longfin eel (Anguilla dieffenbachii) also became less abundant in the cleared reaches, but elvers (Anguilla spp.) became more abundant. In the second case study, pastoral sections in two small streams draining from native forest catchments were restored in 1995/96 by planting riparian vegetation and preventing stock access. After 10 years, the restoration efforts had more than doubled the numbers of giant kokopu (G. argenteus) and redfin bullies (Gobiomorphus huttoni), slightly increased numbers of banded kokopu (G. fasciatus), and decreased shortfin eel (A. australis) numbers by about 40%. The macroinvertebrate communities changed so that they became more similar to those at upstream native forest reference sites. These two case studies show that riparian margins can influence the composition of the fish and macroinvertebrate communities in small streams through the effects on cover, instream habitat and probably water temperature. Riparian restoration was most effective for the fish species that use cover and pool habitat.

Effects of small ponds on stream water quality and macroinvertebrate communities

Six small constructed ponds (surface area 500–7500 m2, catchment area 28–158 ha) in rural and native forest catchments in the Auckland region had poorer water quality than the streams they replaced. Temperature (24°C) and dissolved oxygen (DO) (4 mg/litre) criteria were exceeded for up to 46% and 84% of days, respectively, during a critical 40‐day summer period. The poor conditions found in ponds, even within undeveloped native forest catchments, indicated that the physical characteristics of ponds (e.g., lack of shade, organic sediments) affected water quality independently of other factors (e.g., land use, riparian protection). The frequency and severity of the exceedences were related to pond size, retention time, and catchment land use; the most degraded conditions were found in rural ponds with largest surface areas and longest retention times. Ponds affected water quality and macroinvertebrate communities downstream. Exceedences of temperature and DO criteria occurred more frequently and were more severe downstream than upstream of ponds. Ponds in rural catchments increased mean daily stream temperatures 3.1–6.6°C during the critical summer period, and temperature differences were three times higher than those in bush catchments (0.8–2.0°C). Elevated temperatures were observed for hundreds of metres downstream owing to the slow rate of cooling (1°C/ 100 m), expanding the extent of adverse effects well beyond the “footprint” of the pond. Macroinvertebrate community composition (sample area 1–3 m2) and values of four commonly used metrics appeared to be significantly affected by ponds in rural and native forest catchments. These finding have important management implications that should lead to modifications (e.g., breaching dams) of the estimated 4500 existing ponds in the Auckland region, where possible, and restrictions on proposals for new “on‐line” ponds.

Detecting patterns in hyporheic community structure: Does sampling method alter the story?

Hyporheic invertebrates were sampled in six small headwater streams draining pine, pasture, and native forest catchments. Sites were sampled in autumn and spring using three different hyporheic sampling methods (colonisation pots, pump sampling, and freeze‐coring). Total invertebrate abundance and taxon richness differed significantly among sites on both sampling occasions for pump samples, whereas freeze‐coring did not discriminate among sites, and pot samples showed significant differences in autumn, but not in spring. Differences among sites with respect to community composition were not consistent between sampling methods. Community ordination indicated that samples from colonisation pots tended to group together, whereas pump and freeze core samples were widely separated. Differences across land uses were also apparent (native forest sites formed a distinct cluster separated from pine and pasture sites). Results suggest that colonisation pots may provide a pathway for the entry of epigean organisms into the hyporheic zone even when hydraulic connectivity between surface and hyporheic zones is low. Invertebrate abundance was very low in pump samples, and this method also captured the fewest taxa of the three methods. The size bias known to exist with pump sampling techniques may restrict the usefulness of the method when comparing streams of differing hydraulic conductivity.

Effects of dairying on water quality of lowland streams in Westland and Waikato

Several New Zealand studies suggest that pastoral land use causes appreciable water quality degradation particularly in lowland streams. The water quality of eight NZ lowland streams, three near Morrinsville in the Waikato Region and five south of Hokitika in Westland, was sampled monthly for 13 months. Three of the five Westland streams are spring-fed streams on dairy-farmed alluvial plains of large rivers, and have high and steady flows and visually clear water, contrasting with two nearby reference streams in forested land which are more flow-variable and have humic-stained water. The catchments of the three Waikato streams, with the exception of a forested headwater area, are intensively grazed, mostly by dairy cows. Median conductivity, phosphorus and nitrogen concentrations, and (to a lesser extent) faecal contamination (as indicated by Escherichia coli concentrations), were all elevated in streams draining dairy pasture, often exceeding water quality guidelines. The most intensively-farmed Waikato stream (Toenepi Stream) has very high concentrations of nutrients and fairly high faecal contamination. At the other extreme, Dunlop Creek (Westland) has very low concentrations of nutrients and faecal contamination, consistent with its minimally-disturbed native forest catchment. The optical variables: humic concentration, turbidity and (inversely related) visual water clarity, show less of a pattern with land use across stream sites, apparently because of the influence of other factors, such as soil characteristics. The area-specific yields of streams in Westland dairy land were comparable with those in the Toenepi Stream, reflecting high rainfall driving runoff and leaching in Westland. However, the concentrations of contaminants mobilised by dairy farming were generally higher in Waikato than in Westland because of dilution in high water flows in the latter region. The water quality degradation of streams draining dairy land will need to be addressed by the dairy industry. Keywords: dairying, faecal contamination, nitrogen, nutrients, phosphorus, turbidity, water quality

Factors controlling litter input dynamics in streams draining pasture, pine, and native forest catchments

The effects of varying land use on the inputs of litter to streams were investigated in nine small Waikato, New Zealand, hill country streams between June 1995 and October 1997. Mass, timing, and composition of both vertical and lateral litter inputs were measured. Litter inputs to pasture streams were lower than those to streams in native or exotic pine forest. Litter inputs to native forest streams peaked in summer, with leaf material forming the dominant litter‐type throughout the year. The pine forest sites showed a winter minimum, with a pulse of reproductive litter (pollen heads) in spring. One pasture site, where riparian vegetation included willow and poplar showed an autumnal peak, with low inputs at other times of the year. Climate variables (air temperature, rainfall, and windrun) varied in their power of prediction of litter inputs. Mean air temperature showed a strong positive relationship with monthly litter input at the most intensively sampled native forest site. Annual litter inputs were positively related to canopy cover, although canopy‐type modified this relationship. At several sites lateral inputs of litter showed a positive relationship with the slope of the contributing area. Overall, lateral inputs were positively related to % unvegetated groundcover. In open pastures the combination of a lack of riparian trees, and the potential litter‐trapping capacity of pasture grasses, severely limits inputs of coarse particulate organic matter to streams.

Effects of land use and riparian flowpath on delivery of dissolved organic carbon to streams

A set of near‐stream flowpaths in pasture, native forest and exotic pine plantations in New Zealand was sampled to describe differences in dissolved organic carbon (DOC). The quantity and bioavailability of DOC varied among flowpaths in different land uses, with higher concentrations of DOC in near‐stream flow paths than the parent groundwater emerging from the hillslope. Tiles incubated in these waters did not consistently yield higher bacterial growth rates than tiles incubated in groundwaters. DOC composition, measured as fluorescence and absorbance properties and extracellular enzyme fingerprints, differed significantly among land uses and position along flowpath. Differences in riparian vegetation can indirectly affect DOC by altering exposure to ultraviolet radiation. A 2‐h exposure of water from subsurface flowpaths to full sunlight caused marked changes in fluorescence characteristics of water from the pasture catchment but only small changes in water from the native forest catchment. There were up to fivefold differences in extracellular enzyme activities on tiles incubated in light‐exposed water for the native forest site, but not for the pasture site. Bacterial growth and respiration were higher on tiles incubated in native forest water exposed to sunlight, but there was no light effect on growth for tiles incubated in water from the pasture flowpath. These results indicate that riparian flowpaths will affect the quantity and character of DOC delivered to streams and ultraviolet exposure may, at least in some cases, alter DOC bioavailability.

Interactions of Adult Stoneflies (Plecoptera) with Riparian Zones I. Effects of Air Temperature and Humidity on Longevity

The effects of constant air temperature and relative humidity on the longevity of three species of gripopterygid stonefly adults from New Zealand were investigated in laboratory experiments, and the results were compared to field measurements of air temperature and humidity obtained during summer. Greatest longevity for Zelandobius furcillatus, Zelandoperla decorata and Acroperla trivacuata was recorded in cool humid conditions (10°C, 100% humidity) for adults fed water and a 5% sucrose solution. Absence of feeding reduced survival by 37–73% at 17°C and 100% humidity. Survival decreased significantly with increasing constant air temperature (10, 17 and 25°C) and decreasing mean relative humidity (100, 81 and 15%). Males survived significantly longer than females in all temperature treatments for Z. furcillatus, but longevity was not influenced by gender in other species or in the humidity experiments. Interpolated LT 50 values over 96 h for female stoneflies in the temperature treatments averaged of 22–23°C. Field measurements at near-ground level and 1.5 m above the streambank during summer indicated that these air temperatures were exceeded for 25% of the time in a pasture catchment compared to <0.1% of the time in a native forest catchment. These findings implicate air temperature as a factor potentially influencing the longevity of adult stoneflies, and suggest that maintenance of appropriate microclimate conditions should be a consideration in riparian management.

Hydrology and related changes after harvesting native forest catchments and establishing pinus radiata plantations. Part 2. The native forest water balance and changes in streamflow after harvesting

AbstractSix small, steep, south‐west facing catchments (1.63–4.62 ha) have been monitored in Westland, New Zealand since 1974. Two catchments were retained in native mixed evergreen forest and the rest were subjected to various harvesting and land preparation techniques before being planted with Pinus radiata between 1977 and 1980.The 11‐year water balance for the native forest catchments was: rain = streamflow + interception loss + transpiration + seepage (2370mm = 1290mm + 620mm + 360mm + 100mm). In the year after treatment streamflow generally increased by 200–250 mm, except for one treatment (clearfelling, herbicide application, no riparian reserve) where the increase was 550 mm. The catchments were planted with Pinus radiata, but rapid colonization by bracken (Pteridium esculentum) and Himalayan honeysuckle (Leycesteria formosa) led to a rapid decline in streamflow, which returned to pre‐treatment levels after an average of about five years. Streamflow yields then continued to decline for another two to three years before stabilizing at a level about 250mm yr−1 lower than pre‐treatment levels. At this time the catchments had a dense bracken/honeysuckle understorey beneath 5 m tall pine trees.

Hydrology and related changes after harvesting native forest catchments and establishing pinus radiata plantations. Part 3. Stream temperatures

AbstractEight small steep south‐west facing catchments (1‐63‐8‐26 ha) have been monitored in Westland, New Zealand since 1974. Two catchments were retained in native mixed evergreen forest and the rest were subjected to various harvesting and land preparation techniques before being planted with Pinus radiata between 1977 and 1980. Stream temperatures were measured in all catchments for 11 years, including up to four years before harvesting.The streamwater temperature regime under the native forest cover has a seasonal cycle, with an annual mean of about 9°C and mean daily temperatures ranging between a winter minimum of about 5.8°C and a summer maximum of 12.S°C. After harvesting, the winter minimum stream temperatures in all trials were unchanged as topography exerts the major control over incoming solar radiation. The largest rises in mean summer stream temperatures, up to 5.5°C, were in the catchments that had been clearcut and burnt before planting. The maximum stream temperature recorded was 22.8°C in a clearcut catchment with no riparian reserve. Summer stream temperatures in this catchment were up to 11°C higher than in an adjacent control catchment. Summer stream temperature rises in catchments with riparian reserves were less than 1.5°C.Seven years after harvesting, stream temperatures were dropping towards pre‐treatments levels in only two of the six treated catchments as revegetation of the riparian areas occurred and the plantations became established.As these small headwater streams discharge into streams with flows one or two orders of magnitude larger, the increases in summer stream temperatures will be rapidly dissipated. However, the cumulative impact of harvesting many small headwater catchments that discharge into a larger stream could have a noticeable effect on stream temperature if intact riparian reserves were not retained in both headwater and main streams.

Hydrology and related changes after harvesting native forest catchments and establishing pinus radiata plantations. Part 1. Introduction to study

AbstractThe hydrology of eight small catchments (1.63–8.26 ha) has been monitored in Westland, New Zealand since 1975. Two of these catchments were left in indigenous beech‐podocarp‐hardwood forest and the rest were subjected to various harvesting and land preparation treatments before being planted with Pinus radiata. This paper introduces a series of papers on the hydrology of the indigenous forest catchments and the changes that occurred after treatment. The catchments, experimental programme, climate of the area and the rainfall regime experienced between 1975 and 1987 are described.

Nitrogen and phosphorus in streamwaters from adjacent pasture, pine, and native forest catchments

Abstract Measurements were made of nitrogen (N) and phosphorus (P) concentrations in streams draining three adjacent catchments of different land use. Generally, the pasture catchment stream showed highest concentrations of N and P, compared to the streams draining the pine and native catchments. Total N export coefficients (kg km‐2 year‐1) were estimated as 1195, 131, and 367 for the pasture, pine, and native catchments, respectively. Total P export coefficients (kg km‐2 year‐1) were estimated as 167, 9.5, and 12.0 for the pasture, pine, and native catchments, respectively. Exports of N and P from the pasture catchment were unevenly distributed through the year, with most export occurring as particulate forms during storm events. By comparison, export from the two forested catchments was more evenly distributed and baseflow dissolved forms of N and P formed a higher proportion of total export. The influences of land use were attributable to differences in hydrology, source materials of N and P available ...