The stream hydrology response of converting a headwater pasture catchment to Pinus radiata plantation

ABSTRACT

The planting of degraded land with tree plantations may be effective at improving land use sustainability and profitability but it can also have significant effects on stream hydrology. In this paired catchment study, we report the stream hydrological response to partial (62%) afforestation of a steep pastoral catchment in the western Waikato Region, North Island, New Zealand. We comprehensively analyse the hydrological regime changes over a 23-year period (including eight years before pine planting) with reference to a native-forested ‘control’ catchment. Our results show that afforestation has markedly affected stream hydrology. Seven years after planting, the total annual runoff was 380?mm lower than predicted for the catchment in pasture. Two phases of plantation thinning resulted in the difference between measured and predicted runoff reducing to only 129?mm. Peak flows reduced by ～50% while total stormflow reduced by ～30% – which we attribute to canopy interception attenuating and delaying water yield. The impact of plantation establishment on low flows is not so clear, although afforestation appears to have reduced low flows by ～25%. This study provides information on the hydrological impact of afforestation within a hitherto poorly-represented New Zealand environment (i.e. high rainfall, sedimentary lithology-based, North Island hill country).     

Weak ties, immigrant women and neoliberal states: Moving beyond the public/private binary

This paper engages with the vacillations in provincial and federal gender specific service funding in Canada between 2001 and 2007. I connect this state scale analysis to local settlement experiences of Sikh immigrant women living in a small British Columbia community. Using the concept of network analysis, particularly the idea of weak ties, I offer a corrective to the overly positive appraisals of strong ties and institutional completeness. I argue that experiences of settlement, especially in cases where women face various forms of domestic violence, are shaped by the articulation of neoliberalism and patriarchy. This analysis contributes to the ongoing reformulation advanced by feminist geographers with regard to the public/private binary. In its place this case study reveals the multiple public and private intersections and continuums that exist, and how the recognition of these geographies can assist in building effective public resources to tackle the challenges faced by some immigrant women.     

Cryptic Blooms: Are Thin Layers the Missing Connection?

Harmful algal blooms (HABs) are common in Monterey Bay, CA, and have resulted in repeated closures of shellfish fisheries and the poisoning and death of marine mammals. In the majority of instances, HAB events in this region are first detected by the presence of sick or dying animals. The phrase “cryptic blooms” was adopted to denote the appearance of poisoning at higher trophic levels with no prior evidence of a large phytoplankton bloom. We hypothesize that the onset of many HAB events goes undetected because the bloom is initially concentrated in discrete thin subsurface layers in the water column that are easily missed by conventional sampling and monitoring methods. In this paper, we report on the detection and monitoring of a subsurface layer of phytoplankton in northern Monterey Bay, CA, using a high-resolution, autonomous profiler. This ‘thin layer,’ which measured from 10 cm to 3 m in thickness (85% < 2 m; 54% < 1 m), persisted over a 7-day period near the base of the pycnocline. The phytoplankton assemblage in the layer was primarily composed of a multi-species assemblage of Pseudo-nitzschia including the toxin-producing species Pseudo-nitzschia australis. Concentrations of toxic phytoplankton (P. australis), cyanobacteria, and bacteria in the layer were significantly higher than outside the layer (P < 0.05). Counts of total Pseudo-nitzschia spp. showed similar levels of enrichment in the layer compared to outside the layer. Our findings indicate that, when monitoring for HABs, it is critical to sample at scales appropriate to resolve thin layers. Thin layers have been identified as a common recurrent feature in a variety of coastal systems, suggesting that the use of autonomous high-resolution vertical profilers coupled with targeted sampling, could allow more timely detection of HABs in many coastal environments.     

Ecological Impact of the Introduction to New Zealand of Asian Date Mussels and Cordgrass—The Foraminiferal,Ostracod and Molluscan Record

The ecological impact from the establishment of dense intertidal beds of introduced Asian date mussels (Musculista senhousia) and cordgrass (Spartina alterniflora) in five northern New Zealand estuaries and harbours was documented in 2005–2006, using the fossil record of the shells of foraminifera, ostracods and molluscs in paired sediment cores and surface samples taken from inside and outside selected beds. The most significant changes in faunal composition in all, but the most saline sites, generally occurred in both cores in each pair and could be attributed to the impact of decreased salinity and pH as a result of increased freshwater runoff following clearance of the surrounding forest in the 19th century and urban development in the late 20th century. Establishment of Asian date mussel beds had a greatest impact on the composition of ostracod faunas. At near oceanic salinity, the mussels had completely replaced the native infaunal bivalve fauna, but had little impact on the foraminifera. At more brackish sites, the presence of mussel shells appears to have buffered the calcareous foraminifera from the effects of lowered pH, which had dissolved this component outside the beds. Establishment of cordgrass patches had no impact on ostracod faunas, and little on molluscs except at Kaipara, where introduced Pacific oysters had colonised the cordgrass. Cordgrass had the most impact on the foraminifera. At brackish sites, cordgrass patches had been colonised by agglutinated foraminiferal species different from those that dominate outside. In cordgrass at more saline sites, agglutinated foraminifera have invaded and bloomed at the expense of calcareous Ammonia spp., which dominated outside the patches.     

High‐frequency precipitation and stream water quality time series from Plynlimon,Wales: an openly accessible data resource spanning the periodic table

This scientific briefing announces the availability of a new multi‐element high‐frequency water quality data set that is openly accessible to the research community. The data set comprises up to 2 years of 7‐hourly water quality data for two streams and one rainfall site in the Upper Severn catchment at Plynlimon in Mid‐Wales. The measurements cover 50 analytes ranging from H⁺ to U and spanning six orders of magnitude in concentration, including major, minor and trace elements as well as nutrients, and they complement decades of weekly measurements of the same analytes at the Upper Severn. Together, the weekly and 7‐hourly time series provide a unique data set for studying both long‐term trends and short‐term dynamics. The data show complex behaviour over a wide range of timescales, challenging our understanding of catchment processes and informing future modelling efforts. Copyright © 2013 John Wiley & Sons, Ltd.     

Interacting physical,chemical and biological forcing of phytoplankton thin-layer variability in Monterey Bay,California

During the 2005 Layered Organization in the Coastal Ocean (LOCO) field program in Monterey Bay, California, we integrated intensive water column surveys by an autonomous underwater vehicle (AUV) with satellite and mooring data to examine the spatiotemporal scales and processes of phytoplankton thin-layer development. Surveying inner to outer shelf waters repeatedly between August 18 and September 6, the AUV acquired 6841 profiles. By the criteria: [(1) thickness ≤3 m at the full-width half-maximum, (2) peak chlorophyll at least twice the local background concentrations, and (3) a corresponding peak in optical backscattering], thin layers were detected in 3978 (58%) of the profiles. Average layer thickness was 1.4 m, and average intensity was 13.5 μg l^?1 above (3.2x) background. Thin layers were observed at depths between 2.6 and 17.6 m, and their depths showed diurnal vertical migration of the layer phytoplankton populations. Horizontal scales of thin-layer patches ranged from <100 m to>10,000 m. A thin-layer index (TLI), computed from layer frequency, intensity and thinness, was highest in mid-shelf waters, coincident with a frontal zone between bay waters and an intrusion of low-salinity offshore waters. Satellite observations showed locally enhanced chlorophyll concentrations along the front, and in situ observations indicated that phytoplankton may have been affected by locally enhanced nutrient supply in the front and concentration of motile populations in a convergence zone. Minimum TLI was furthest offshore, in the area most affected by the intrusion of offshore, low-chlorophyll waters. Average thin-layer intensity doubled during August 25–29, in parallel with warming at the surface and cooling within and below the thermocline. During this apparent bloom of thin-layer populations, density oscillations in the diurnal frequency band increased by an order of magnitude at the shelfbreak and in near-bottom waters of the inner shelf, indicating the role of internal tidal pumping from Monterey Canyon onto the shelf. This nutrient transport process was mapped by the AUV. Peak TLI was observed on August 29 during a nighttime survey, when phytoplankton were concentrated in the nutricline. Empirical orthogonal function decomposition of the thin-layer particle size distribution data from this survey showed that throughout the inner to outer shelf survey domain, the layers were dominated by phytoplankton having a cross-section of ～50 μm. This is consistent with the size of abundant Akashiwo sanguinea cells observed microscopically in water samples. During a subsequent and stronger intrusion of low-salinity offshore waters, spatially-averaged vertical density stratification decreased by > 50%, and phytoplankton thin layers disappeared almost completely from the AUV survey domain.     

Fine scale variations of surface water chemistry in an ephemeral to perennial drainage network

Although temporal variation in headwater stream chemistry has long been used to document baseline conditions and response to environmental drivers, less attention is paid to fine scale spatial variations that could yield clues to processes controlling stream water sources. We documented spatial and temporal variation in water composition in a headwater catchment (41 ha) at the Hubbard Brook Experimental Forest, NH, USA. We sampled every 50 m along an ephemeral to perennial stream network as well as groundwater from seeps and 35 shallow wells across varying flow conditions. Groundwater influences on surface water in this region have not been considered to be important in past studies as relatively coarse soils were assumed to be well drained in steep catchments with flashy runoff response. However, seeps displayed perennial discharge, upslope accumulated areas (UAA) smaller than those for channel initiation sites and higher pH, Ca and Si concentrations than streams, suggesting relatively long groundwater residence time or long subsurface flow paths not bound by topographic divides. Coupled with a large range in groundwater chemistry seen in wells, these results suggest stream chemistry variation reflects the range of connectivity with, and quality of, groundwater controlled by hillslope hydropedological processes. The magnitude of variations of solute concentrations seen in the first order catchment was as broad as that seen at the fifth order Hubbard Brook Valley (3519 ha). Reduction in variation in solute concentrations with increasing UAA suggested a representative elementary area (REA) value of less than 3 ha in the first order catchment, compared with 100 ha for the fifth order basin. Thus, the REA is not necessarily an elementary catchment property. Rather, the partitioning of variation between highly variable upstream sources and relatively homogenous downstream characteristics may have different physical significance depending on the scale and complexity of the catchment under examination. Copyright © 2012 John Wiley & Sons, Ltd.     

Towed vehicle observations of thin layer structure and a low-salinity intrusion in Northern Monterey Bay,CA

Thin phytoplankton layers are common features in the coastal environment; however sampling these fine-scale optical features across broad horizontal scales remains a challenge. To investigate the horizontal spatial structure of thin phytoplankton layers, we performed an overnight survey in northern Monterey Bay, CA, USA using a SeaSciences Acrobat towed-vehicle. Physical and optical measurements were collected between the surface and near-bottom-depths along four parallel, across-shore transects. Three coherent chlorophyll features were observed: (1) a broad, sub-surface patch at the offshore end, (2) a near-surface patch at the nearshore end, and (3) a deep patch located between the nearshore and offshore patches. The offshore and nearshore patch were separated by a change in seafloor slope and a region of compressed, shoaling isopycnals. Both the offshore and nearshore features were located at the pycnocline, had similar optical properties, and were co-located with a low-salinity intrusion. The deep chlorophyll patch had associated physical and optical properties that were distinct from the patches at the pycnocline. The results from this study further underscore the heterogeneous horizontal spatial structure of thin layers and also add to the growing evidence suggesting that low-salinity intrusions may be strongly linked to the formation of thin phytoplankton layers over the northern shelf of Monterey Bay.     

Holocene valley-floor deposition and incision in a small drainage basin in western Colorado, USA

The valley floor of a 33.9 km² watershed in western Colorado experienced gradual sedimentation from before ∼ 6765 to ∼ 500 cal yr BP followed by deep incision, renewed aggradation, and secondary incision. In contrast, at least four terraces and widespread cut-and-fill architecture in the valley floor downstream indicate multiple episodes of incision and deposition occurred during the same time interval. The upper valley fill history is atypical compared to other drainages in the Colorado Plateau.One possible reason for these differences is that a bedrock canyon between the upper and lower valley prevented headward erosion from reaching the upper valley fill. Another possibility is that widespread, sand-rich, clay-poor lithologies in the upper drainage limited surface runoff and generally favored alluviation, whereas more clay-rich lithologies in the lower drainage resulted in increased surface runoff and more frequent incision. Twenty-two dates from valley fill charcoal indicate an approximate forest fire recurrence interval of several hundred years, similar to that from other studies in juniper-piñon woodlands. Results show that closely spaced vertical sampling of alluvium in headwater valleys where linkages between hillslope processes and fluvial activity are relatively direct can provide insight about the role of fires in alluvial chronologies of semi-arid watersheds.