Riparian management affects instream habitat condition in a dairy stream catchment

Using a space-for-time substitution design, we investigated the response of structural instream habitat and fish populations to different riparian management practices throughout a Dairy Best Practice Catchment. We found a significant negative correlation between the upstream area of stock exclusion fencing and deposited instream fine sediment cover. Furthermore, we determined that this relationship emerges when ≥300?m lengths of upstream riparian area were included in the analysis, indicating the scale at which stock exclusion fencing results in a positive instream habitat response. Specifically, for this historically degraded spring-fed stream, our findings indicate that riparian segments with 5 m wide stock exclusion fences (both banks) are required to achieve instream fine sediment cover below 20% in downstream reaches. Fish were sparse and evenly spread throughout the catchment. Fish distributions were not correlated with reach-scale riparian or instream habitat variables, possibly because the available habitat quality gradient was too narrow.     

Stream channels are narrower in pasture than in forest

In the Hakarimata Range, west of Hamilton, New Zealand, second‐order streams appear to be wider in native than in pasture catchments, whereas streams in pine plantations (18 years old) appear to be suffering active stream‐bank erosion. A working hypothesis to explain these observations was that pasture vegetation replacing original forest encroaches on the stream channel, causing it to become narrower. To test the hypothesis, channel widths were measured up stream and down stream of “transitions” from native forest to pasture in 20 streams of different size in marginal ranges of the Waikato Basin. Small streams (catchment area <1 km², width in forest <2 m) were found to be half the width in pasture reaches as in forest. The degree of channel narrowing decreased as stream size increased and was minimal in large streams (catchment area >30 km², width in forest >10 m). This narrowing of stream channels implies that native forest clearance in New Zealand has reduced stream channel habitat. A concern regarding riparian planting for stream restoration is that sediment stored in pasture stream banks could be mobilised if grasses are extinguished by shading, resulting in turbid streamwater and sedimentation of fines in the channel.     

Predicting spatial patterns in riverbank erosion for catchment sediment budgets

Riverbank erosion is an important component of catchment sediment budget models but remains one of the least well-understood processes, particularly at large spatial scales. Here, we develop and test a new bank migration model in New Zealand for large catchment applications that (1) better represents spatial variability in factors influencing bank erosion and (2) improves predictive performance. We represent bank migration rates as a function of reach-scale stream power, channel sinuosity, soil texture, valley confinement, riparian woody vegetation and channel protection works. The new model significantly improves prediction compared to the SedNetNZ model. Comparison of measured bank migration rates with individual variables shows percent silt + clay derived from soil maps exhibited the strongest correlation, whereas other variables were non-significant. The model results demonstrate that improved prediction can be achieved by combining spatial representation of multiple factors over large areas, despite low correlation between individual variables and bank migration 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.     

Predicting the effects of shade on water temperature in small streams

A computer model for stream water temperature was developed, and tested in a small pasture stream near Hamilton, New Zealand. The model quantifies shading by riparian vegetation, hillsides, and stream banks using three coefficients: canopy angle, topography angle, and canopy shade factor. Shade was measured directly and found to vary significantly along the channel. Using the maximum measured shade, a close match was achieved between observed and predicted daily maximum and minimum water and bed sediment temperature. Model predictions of incoming and outgoing long‐wave radiation flux closely matched measurements, but there were unexplained discrepancies in short‐wave radiation flux. Model predictions indicate that moderate shade levels (c. 70%) may be sufficient in temperate climates to restore headwater pasture stream temperatures to 20°C, an estimate of the thermal tolerance for sensitive invertebrates.     

Riparian protection and on‐farm best management practices for restoration of a lowland stream in an intensive dairy farming catchment: A case study

Abstract

Poor water quality (high concentrations of nitrogen (N), phosphorus (P), suspended solids (SS), and faecal bacteria) in Waiokura Stream, southern Taranaki, New Zealand, is attributed to diffuse and point source (PS) inputs from dairy farming. Trend analysis of concentration time‐series data (2001–2008) and annual yields (i.e., stream load divided by catchment area) showed that significant improvements occurring since 2001 may be attributed to changes in farming practices and riparian management. Yields of filterable reactive P, total P and SS declined by 25–40% as a result of increased riparian protection, a reduction in dairy shed effluent (DSE) pond discharges from 8 to 6 with conversion to land irrigation, and a 25% reduction in the average application rate of P fertiliser. Median annual Escherichia coli concentrations declined at a rate of 116 per 100 ml per year, as a result of fewer PS discharges and improved riparian management. Thus, improvements in stream water quality were attributed to adoption of on‐farm best management practices, fewer DSE discharges and riparian management involving permanent livestock exclusion from stream banks and riparian planting to mitigate runoff from pasture. During 2001–06, N fertiliser use increased by 30% and, with a 130% increase in supplementary cattle feed during 2003–08, led to an increase in average milk solids production 1021 to 1262 kg ha^?1 during 2001–06 with the increased production likely associated with increased N leaching losses. Total N and nitrate‐N concentrations and yields increased during 2001–07 as a result of the intensification in land use and increased N cycling. Stream invertebrate surveys using the macroinvertebrate community index (MCI) metric showed little improvement in MCI during 2002–07, probably because of the relatively short timeframe of this study and because water temperatures were not a limiting factor for invertebrate communities. The absence of native forest streams in the proximity of Waiokura Stream that might act as sources of sensitive species to recolonise the restored stream should also be considered as a constraint to improvements in biological community structure.     

Water quality in a polluted lowland stream with chronically depressed dissolved oxygen: Causes and effects

Abstract

The Whangamaire Stream (North Island, New Zealand) has high concentrations of nitrate nitrogen (NO^? ₃‐N), biochemical oxygen demand (BOD₅), and Kjeldahl nitrogen (TKN) as a result of catchment land use practices. The lower reaches of the stream drain intensively farmed land and have dissolved oxygen (DO) levels of 10–50% saturation. The dominant riparian vegetation, Apium nodiflorum, provides a large organic loading by intercepting nutrients in run‐off and then decaying in the stream channel. Water quality and reaeration aspects of the stream were studied in order to explain the observed low DO levels. Measurements of the reaeration coefficient at 20°C, K₂ ²⁰, using methyl chloride (CH₃Cl) as a gas tracer, yielded values of 1.1–3.0 d^?1 for the upper part of the study reach and 15.5–16.2 d^?1 for the lower reach (overall average 12.5 ± 2.5 d^?1). These were in agreement with values inferred from single‐station diurnal curve analysis, which also showed that respiration was dominant in the lower reach where photo‐synthetic activity was inhibited by shade. The relatively large reaeration coefficients ensure that parts of the stream do not become anoxic at night time. Better riparian management and reduced nutrient inputs are likely to improve stream water quality.     

Coastal conditions in West Africa—A review

This paper describes the coastal system between Cape Palmas bordering the Ivory Coast and Liberia and Mount Cameroon, as a basis for regional coastal-erosion management.The area includes the rocky coasts of the Ivory Coast and Ghana, the long sandy beaches of Togo and Benin and the deltas of the Volta and Niger Rivers. Important elements of the system appear to be its geographical setting, its geological history, oceanological impacts, the sediment supply by rivers and coastal erosion, littoral transport and the rise of mean sea level. The morphological processes are influenced by human activities in the catchments of the rivers (dams), in the estuaries (dredging) and along the coasts (port construction).It appears that future human interventions and the impact of increased sea-level rise will require intergovernmental co-ordination in coastal-erosion management, as the various coasts are all part of one system.     

Formation of sand banks due to tidal vortices around straits

Sand banks around straits are used as a commercial fishing ground. In order to clarify the mechanism of sand bank formation, the Lagrangian method was used to measure currents and turbidity around the banks in the Neko Seto Sea in the Seto Inland Sea of Japan. A neutrally buoyant float released in the Neko Seto Strait at the maximum tidal flow stage was engulfed in a pair of tidal vortices and moved around one of the sand banks. The vertical distribution of turbidity, which was measured by the vessel moving with the neutral float, showed an extremely high turbidity in the bottom layer of this bank area. According to the analysis of these observational data, the process of sand bank formation around straits is as follows. The tidal vortex transports water mass with suspended materials (including sand) which are whirled up at the bottom by the tidal jet. In the decaying stage of the vortex, the materials in the bottom layer are gathered in the central part of the vortex by the secondary convergent flow in the vortex. Among these materials, a large-size sand particle with a high critical erosion velocity accumulates at the bottom and forms banks. The distribution of bottom sediment and the thickness of alluvium support this result.     

Modelling the time course of shade,temperature, and wood recovery in streams with riparian forest restoration

Action is increasingly being taken in New Zealand and elsewhere to restore ecological function to streams through planting of riparian zones. We used simulation modelling to explore the relative performance of three strategies to restore the riparian zone of a pastoral stream to native forest by: (1) passive regeneration; (2) planting then abandonment of a Pinus radiata plantation; and (3) active restoration by planting selected native trees. We linked the forest model LINKNZ with a shade and temperature model (sWAIORA), and a wood model (OSU_STREAMWOOD) to simulate recovery trajectories for key forest stream attributes in hypothetical streams (1.3–14.0 m channel width) in the central North Island, New Zealand. Both active restoration strategies outperformed passive regeneration in shade, temperature and stream wood volume for most of the simulation time (800 years). Although the abandoned pine plantation provided greatest shade initially (<100 years), active native planting provided the greatest benefits overall. In general, recovery of stream shade (and temperature) is expected within decades, is accelerated by deliberate planting, and is fastest in small streams in which thermal stress from sunlight exposure is greatest. However, full recovery of stream and riparian function may take centuries, being dependent on large trees providing wood to structure the channel.     

长江口南汇边滩冲淤变化规律与机制

根据1842—2004年海图资料分析发现,南汇边滩存在近百年尺度的强烈冲刷—淤积旋回。长江主泓走南港或北港是造成冲刷期"北滩、东滩淤积,南滩、过渡带冲刷"或淤积期冲淤态势反相的主要原因;冲刷期内风暴强度和频数明显多于淤积期,造成冲刷期滩面叠置记忆的是暴风浪成因的"高滩冲刷、低滩淤积"的冲淤态势,而淤积期保存的是弱风浪成因的"高滩淤积、低滩冲刷"叠置增强的剖面特征。尽管三角洲整体冲淤态势的转变主要受流域来沙量的控制,但不同岸段受河口河势分水分沙作用、潮流和波浪等共同作用,明显存在此冲彼淤、冲淤动态调整等特征。已有的入海泥沙含量阈值研究以点代面或以局部代整体,这是造成阈值估算偏高的主要原因。2003年三峡水库开始蓄水后平均年输沙量154 Mt/a已低于低阈值184 Mt/a,但三角洲尚未如预测那样发生由净淤积向净侵蚀的转变。已有的河口水文观察资料显示,水体含沙量也未发生明显下降,这可能是潮控型三角洲潮流对泥沙在河口的再分配起主导作用,并可能由此延长三角洲冲淤转变对入海泥沙量减少的滞后。今后需进一步加强潮控型河口复杂过程的综合研究,提高对泥沙含量阈值估算和应对可能面临的海岸侵蚀及其相关的环境地质灾害的能力。     

Trialling tools using hand-weeding,weed mat and artificial shading to control nuisance macrophyte growth at multiple scales in small agricultural waterways

ABSTRACT

Introduced aquatic macrophytes can dominate small agricultural waterways in summer and autumn becoming a significant management problem. Excessive growth can clog waterways, causing drainage issues and reducing agricultural productivity while in-stream velocities are reduced and sedimentation increased. Consequently, water managers remove them by mechanical clearance, chemical spray and cutting which can be costly and have negative impacts on in-stream habitat and ecological health. We trialled three tools to reduce macrophytes: hand-weeding, weed mat and artificial shading, at a reach-scale (50?m) and larger-scale (200–400?m). Hand-weeding reduced cover in the short-term, however macrophytes recovered to pre-treatment levels within one season. Weed mat along the banks was effective at reducing emergent macrophytes, particularly Erythranthe guttata (monkey musk) and Nasturtium microphyllum (watercress). Weed mat lasted for several growing seasons and continued to be effective. Shading over the waterway using polythene markedly reduced submerged macrophytes indicating that heavy shading by riparian plantings could reduce submerged macrophytes in the longer-term. These results indicate that in the short-term, weed mat could be used to limit sprawling emergent macrophytes. In the longer-term, weed mat used in conjunction with riparian planting could provide shading so that macrophyte cover in these small waterways could be reduced and controlled.     

三峡截流以来长江洪季潮区界变动河段冲刷地貌

潮区界河段河势演变对三峡工程的响应是长江经济带建设中的重要问题。然而受观测手段所限,对三峡截流以来潮区界变动范围及其地貌演变的客观认识亟待探讨。对大通站洪季水位资料进行频谱分析,初步判断了近期长江洪季潮区界位置;对比1998年和2013年水下地形资料,分析了三峡大坝截流以来该河段河槽的冲淤演变特征;利用多波束测深系统对冲刷明显河段的微地貌进行了高分辨率观测。结果显示:（1）1998-2013年潮区界变动河段河槽整体冲刷5 649.7万m3。其中,上段全面冲刷,太白、太阳两洲并岸,铜陵沙被冲开,主槽刷深达5.6 m;中段主泓摆动,天然洲南冲北淤,黑沙洲中水道淤死,南水道左岸最大冲深达8.9 m;下段近岸冲刷强烈,北岸最大冲深达15.4 m;（2）该河段近期处于剧烈的冲刷环境,左岸冲刷尤为显著;（3）冲刷深槽分布在顺直河段,深达5.4~12.6 m;冲刷坑分布在分汊河段平面形态突变处,最大冲深达28.1~30.5 m;水下侵蚀陡坡分布在近岸侵蚀严重的顺直河段,坡度为0.59~0.62。     

Heavy metals in Ligurian Sea Sediments: distribution of Cr,Cu, Ni,and Mn in Superficial Sediments

Fifty-six samples of superficial marine sediment collected in the continental shelf area between Arenzano and Capo Noli were examined, along with nineteen fluvial sediment samples from creeks flowing into the area under examination. The materials were subjected to textural and chemical analyses, the latter to determine the Cr, Cu, Ni, and Mn contents using two different procedures.The geology and physiography of the coastal belt were also studied. From the data obtained, maps were drafted showing the distribution of metals: these experimental values were compared graphically to sediment texture values. High values for Cr and Ni were found, justified by stream erosion on basic rock outcrops. Only for Cr was a significant input of artificial origin found. In the case of Cu and Mn, relations with the organic fraction and texture of sediments, respectively, have been evidenced.     

Evaluating practical macrophyte control tools on small agricultural waterways in Canterbury,New Zealand

Excessive macrophytes can cause significant problems in agricultural waterways requiring active management. Conventional control techniques can have a range of adverse effects. We investigated several control tools in two experiments: firstly, we tested eight treatments at a small-scale (2?m?×?2?m). We found intensive hand weeding, weed mat and herbicide spraying to be effective treatments, reducing macrophyte cover to <5%. Hand weeding and weed mat immediately reduced cover, while dieback from herbicide took two months. Weed mat was a novel and effective control mechanism along stream banks. Secondly, we tested the impact of shading on macrophyte growth. Macrophyte growth was enhanced under partially shaded conditions, but with 80% effective shading over the entire channel, cover was reduced to 17%. Once treatments ceased, macrophytes grew back within 3–5 months. Long-term, control methods will require combinations of tools but will need to include optimal shading for the target species.     

Coastal erosion and control

Coastal erosion is a problem at many coastal sites caused by natural effects as well as human activities. This paper explores the coastal cell concept to deal with coastal erosion by identifying and analysingthe sediment volumes accumulated in large-scale and small-scale coastal cells at various sites. Mechanisms causing chronic erosion and episodic erosion related to coastal variability are identified and discussed. The effectiveness of soft and hard remedial measures for sandy beaches are assessed based on laboratory, field and modelling experiences.     

Sediment-related water quality of small hill-country streams near Whatawhata,New Zealand. Response to integrated catchment management (ICM)

ABSTRACT

Degradation of aquatic ecosystems by fine sediment is a global environmental problem, and damages reflect particle properties as well as mass concentration. We studied sediment-related water quality (SRWQ) of small streams in hill-country near Whatawhata, NZ, that have been monitored since 1995. In 2001, an integrated catchment management (ICM) plan was implemented in the Mangaotama (originally sheep-beef) catchment – including conversion of steep headwaters to pine plantation, cattle exclusion, and native riparian plantings. The long-term SRWQ within the Mangaotama catchment was examined with reference to a nearby native-forested control catchment. Correlations between visual clarity, suspended particulate matter concentration and related variables were moderate to fairly strong. The ICM has not improved SRWQ as expected – plausibly because removal of cattle disturbance has been offset by decline in pasture ground cover under increasing shade of tree plantings. Worsening SRWQ is expected over the next several decades as channels widen towards a ‘forest’ morphology.     

Water quality and sediment and nutrient export from New Zealand hill‐land catchments of contrasting land use

Measurements were made of suspended sediment (SS), volatile suspended solids, dissolved organic carbon (DOC), nitrogen (N) and phosphorus (P) concentrations, turbidity, black disk visibility, pH, alkalinity, and temperature, at monthly intervals for 2–5 years on nine streams draining catchments with pasture, pine plantation, and native forest land uses. Stream flow and flow‐weighted concentrations of SS, N, and P were also measured for up to 2 years from pasture, native forest, and mixed land‐use catchments enabling calculation of export (kg ha^‐1 yr^‐1). During 1996–97, export from the pasture stream was 2.5‐ to 7‐fold higher for SS (988), total P (1.50), total Kjeldahl N (5.65), nitrate N (4.37), and ammoniacal N (0.34) than from the stream draining native forest. In contrast, export of DOC (25.5) and dissolved reactive P (DRP) (0.25) from the pasture stream were within 20% of the native stream's values. Export of SS and nutrients (except DRP) from the pasture catchment was 4‐ to 15‐fold higher during the winters of 1995 and 1996 than winter 1997 when rainfall was half the normal level. Streams draining native forest had lower temperature, sediment, and nutrient concentrations (except DRP), and higher water clarity, than those draining pine forest and pasture. A pine/scrub stream had the highest SS and turbidity and lowest DRP, pH, and alkalinity. Pasture streams had the highest concentrations of all N species (geometric means 2‐to 4‐fold > native), total P, and DOC, and also showed the greatest variation in water quality attributes in relation to season and flow. The influences of land use were attributable to differences in both source materials of sediment and nutrients available for transport and changes in rates of in‐stream processing.     

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.