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Tasman Coast: Waimea Inlet to Kahurangi

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Identify the source of the primary stressor (i.e. fine sediment) affecting eelgrass habitat in the region. The assessment found that ~30% of the salt marsh in the Tasman and Golden Bay estuaries (excluding Abel Tasman) has been lost since 1900. Identify the source of the main stress (i.e. fine sediment) affecting salt marsh habitat in region.

Large-scale map of the extent of coastline armor across the region at 5-year intervals.

Table 1.  Coastal Monitoring Tools (Wriggle Coastal Management).
Table 1. Coastal Monitoring Tools (Wriggle Coastal Management).

General

Geology's most significant influence on coastal habitats is whether the rocks in the catchment area are dominated by soft or hard rocks. The largest river in the Tasman region is the Aorere River with a mean flow of 84m3/s (Table 5). Major rivers, catchments and mean streams in the Tasman region (source TDC and NIWA WRENZ data).

Major rivers, catchments and mean streams in the Tasman region (source TDC and NIWA WRENZ data).

Table 4.  Landuse in the Tasman region (from 2007 Agricultural Production Census, Statistics NZ).
Table 4. Landuse in the Tasman region (from 2007 Agricultural Production Census, Statistics NZ).

Habitat Types

The most extensive and active dune systems in the Tasman region apart from Farewell Spit are found on the western coast of Tasman. Unfortunately, the area of ​​active dune area in the Tasman region has declined markedly since 1950 (Hilton 2006). Tide-modified and tide-dominated beaches occur in the more sheltered, macro-tidal Tasman and Golden Bay areas.

Reflecting flat plus sand” is the most common type of beach in the area (eg Ruby Bay, Moutere Bluff, Tapu Bay).

Figure 3   Schematic diagram of healthy coastal dune system Wharariki Beach
Figure 3 Schematic diagram of healthy coastal dune system Wharariki Beach

Overview

Fine Sediment (Muds)

Concentrations of organic matter are generally very high, causing a black to dark gray appearance in the sediments. Surfaces are generally flat and unvegetated, although some seagrass growth in the shallow lower parts of the central basin usually occurs. In the absence of detailed water quality data, the most sound and common sense approach identified is a modification of the Illinois approach (see Table 7).

Determining the existing condition of estuaries and bays is important because current SS input loads may not reflect actual conditions in the estuary.

Figure 4   Conceptual diagrams of different estuary types and susceptibility to fine mud sedimentation   Main mud deposition areas  shown in yellow
Figure 4 Conceptual diagrams of different estuary types and susceptibility to fine mud sedimentation Main mud deposition areas shown in yellow

Nutrients and Eutrophication

In the USA, more comprehensive guidelines have been developed, which include primary and secondary symptoms of eutrophication (Bricker et al. 1999). The US primary and secondary symptoms approach (Bricker et al. 1999) is a comprehensive methodology for reliably detecting symptoms of eutrophication. The US approach (Bricker et al. 1999) identifies the estuary as having excessive concentrations of nutrients, phytoplankton, and macroalgae, but not very high secondary symptoms of low loss of water column chlorophyll a or seagrass—a rating "poor" (slightly eutrophic).

However, the inclusion of the proposed RPD sediment symptoms, sediment nutrients and severe disturbance conditions correctly places the estuary in the eutrophic category.

Table 11.   Existing ‘thresholds’ for assessing eutrophic status . Australia and New Zealand ANZECC (2000) Summer Max Chlor
Table 11. Existing ‘thresholds’ for assessing eutrophic status . Australia and New Zealand ANZECC (2000) Summer Max Chlor

Disease Risk

Therefore, in the absence of more comprehensive data, especially during rain events, the assessment of disease risk was undertaken through a prediction approach based on the following assumptions;. Disease risk to beaches and rocky shores in Tasman and Golden Bays was assumed to be relatively low during river base flow, but sometimes increased during floods, with the greatest risk attributed to beaches near infected river plumes. For beaches and rocky coasts, it can be assumed that there is a disease risk if the habitat is located in a river plume area and the estuary in question has an increased surface FC load.

The assessment also includes an estimate of the likely timing of periods of disease risk (e.g., during floods for watershed runoff sources).

Table 14.  Faecal coliform (FC) yields for different  landuses in New Zealand (Wilcock 2006)
Table 14. Faecal coliform (FC) yields for different landuses in New Zealand (Wilcock 2006)

Toxicants

To assess the vulnerability of estuaries and offshore sediments in the Tasman region to naturally high inputs of heavy metals, the presence of significant areas of ultramafic mineral-rich rocks in catchments is used as a primary indicator (Table 17). Some of these chemicals can remain in the environment and be transported to estuaries and coastal sediments attached to soil particles. Currently, intensive pesticide use in the Tasman region is mainly associated with commercial fruit and vegetable production (Manktelow et al. 2005).

To determine the vulnerability of coastal areas in the Tasman region to oil spills, the following categories are used (Table 19).

Table 17.  Guideline criteria used to assess coastal vulnerability of estuaries and coastal  subtidal deposition areas to naturally occurring inputs of heavy metals
Table 17. Guideline criteria used to assess coastal vulnerability of estuaries and coastal subtidal deposition areas to naturally occurring inputs of heavy metals

Climate Change

An increase of 0.8 million in 2090 corresponds to an average change of +10 mm/year, placing it in the high vulnerability category. The western Tasmanian tidal estuaries and beaches and dunes between Paturau and Kahurangi, Wainui and Puponga and Otuwhero/Marahau all fit into the high to very high category. The majority of the other estuaries and beaches and sand dunes fit in the moderate category, with the Motueka Delta and the beaches between Tapu Bay and Otuwhero fitting in the low category.

These authors also point out that there is an immediate need for monitoring programs to assess impacts on communities, using climate change indicator organisms, as has been done by the MarClim project in the UK (Mieszkowska et al. 2005) and in Southland. New Zealand (Stevens and Robertson 2011).

Table 20.  Physical vulnerability rankings for  climate change - sea level rise.
Table 20. Physical vulnerability rankings for climate change - sea level rise.

Drainage and Reclamation

We review the observed impacts of climate change (eg warming, ocean acidification, changes in storm patterns) on subtidal temperate coasts in Australia and determine how these systems are likely to respond to further change. Observed impacts are region-specific with the greatest number of species responses attributable to climate change in south-eastern Australia, where recent ocean warming has been most pronounced. More importantly, recent experiments suggest that the combined effects of climate change and non-climate stressors (overharvest, reduced water quality) will reduce the resilience of temperate marine communities to disturbances (e.g., storms, disease, and introduced species), many of which are also predicted to increase in frequency and/or severity.

Thus, climate change is likely, both by itself and in synergy with other stressors, to impose changes on southern Australian coastal species, including the important algae that shape the habitat and ecological functioning associated with temperate coasts.

Freshwater Abstraction

Because of the east-west orientation of the south coast, most of Australia's temperate waters are found within a narrow latitudinal band, where any southward movement of isotherms is likely to affect species over very large areas. Future increases in temperature are likely to lead to further distribution shifts of macroalgae and associated species, with distribution contractions and local extinctions to be expected for species that have their northern limits along the southern coastline. Although there is currently no evidence of changes attributable to non-temperature-related climate impacts, possibly due to a lack of long-term observational data, experimental evidence suggests that ocean acidification will have negative effects on calcifying algae and animals.

Because reduced freshwater inflows reduce dilution and flushing, water quality can be expected to decline, and in extreme situations lead to excessive turbidity, eutrophication and disease risk.

Harvesting Living Resources

An increase in turbidity, eutrophication and disease risk symptoms can be expected, affecting especially juvenile fish species that use the estuary as a nursery, high-value seagrass and salt marsh vegetation, and human recreational and shellfish collection uses. Estuaries that are permanently open but include a poorly flushed lagoon (eg Waiau Lagoon in Southland - note Tasman has no examples) are also highly susceptible to ecological damage from withdrawal, particularly as a result of a reduction in flush flow. Estuaries that are permanently open but include deeper areas in the upper estuary where saline bottom water accumulates and has the potential to stagnate unless regularly flushed by high flows (eg Motupipi estuary).

Estuaries that are permanently open and have a very high freshwater inflow:seawater inflow ratio; i.e.

Invasive Species

Structures that disrupt sediment transport

Breakwaters are used to protect harbor entrances and extend from the coastline out to sea. In this case, they are referred to as "detached" exchangers and can be submerged or emergent. Ironically, a major effect of these structures, whether attached or detached, is the creation of currents that can cause downstream coastal erosion, often a considerable distance from the structure.

Apart from the loss of beach habitat directly below the reefs, other impacts may include disruption of sediment supply to downstream sections of the shoreline, increased erosion (Roul and Tondello 2008) and alteration of local hydrodynamics and sediment grain size which may be detrimental. affect the abundance, distribution and diversity of beach fauna (Walker et al. 2008).

Off-Road Vehicles

These structures can be made of concrete blocks, rock piles or dolosses (geometric concrete blocks). The ecological consequences include altered hydrology, which affects the distribution of marine organisms, changes in grain size which affect the abundance and composition of fauna, loss of habitat through erosion (Roul and Tondello 2008), and alteration of habitat through soft substrata with hard structures to replace. . Reefs, which can be constructed of concrete or simply piles of rock, introduce islands of hard substrata into what would otherwise be continuous areas of intertidal sand.

By removing insulating barriers, these structures provide stepping stones for the dispersal of marine biota (including invasive species) normally associated with rocky reefs (Airoldi et al. 2005).

Toxic Algal Blooms

A number of studies have shown that toxic dinoflagellate blooms often coincide with increased rainfall and freshwater runoff, as well as a stable water column (Hallegraeff et al. 1995, Weise et al. 2002). The association of toxic dinoflagellate blooms with freshwater runoff has not yet been elucidated, but may be due to more favorable temperature and salinity conditions, supply of humic substances, increased stability of the water column, or a combination of these. factors that may be physiologically important. for optimal cell growth. The conditions that favor the flowering of Pseudo-nitzschia and other species are also not entirely clear, but the optimal growth conditions are similar to dinoflagellates; that is, a thermally stratified water column, warm surface waters, and high nutrient concentrations (Parsons et al. 2002, Trainer and Hickey 2003, Spatharis et al. 2007, McKenzie et al. 2011).

Poisonous flowers are also commonly associated with freshwater plumes (Franks and Anderson 1992, Hallegraeff et al. 1995).

Table 28.  Toxic algal bloom guideline criteria used to assess coastal water vulnerability
Table 28. Toxic algal bloom guideline criteria used to assess coastal water vulnerability

Dune Overstabilisation

Human/Animal Disturbance of Wildlife

Grazing in High Value Habitat

Loss Of Natural Terrestrial Margin

A small part of the strip (~800 m) is planted with native sand-binding species (spinifex and pingao). Onahau Estuary is a small (32 ha), shallow, well-flushed, seawater dominated, tidal lagoon type estuary with one tidal opening, one main basin, a small tidal arm and a very large area (19 ha, 60%) in salt marshes. , which transitions into freshwater wetlands at the head of the estuary. Two potentially invasive mangrove trees have been planted in the Milnthorpe arm on the north side of the estuary.

Several large barrier spears project to the south and create a relatively stable area in the northern part of the fjord. At low tide, most of the estuary consists of exposed sandy or cobbled intertidal flats. A large part of the Aorere catchment is steep and covered with natural vegetation (80% of the catchment).

But the estuary is very muddy (13% soft mud) and the natural vegetation margin has mostly been lost and developed into pasture (although there is some coastal forest along the western margin) and large parts of the estuary are ringed by roads ( ~5.5 km). The terrestrial margin is dominated by pastoral land use, and much of the estuary catchment is regenerating natural forest (79%), exotic forest (11%) and intensive pastoral use of 9%. However, significant areas of the natural vegetation margin have been lost and the lagoon area is very muddy (11% is soft mud).

A number of other bodies of water (eg Kaihoka Lakes and Lake Otuhie) in close proximity add to the value of the estuarine/freshwater complex for wildlife. The assessment showed that ~30% of the salt marsh in the Tasman and Golden Bay estuaries (excluding the Abel Tasman and Farewell Spit areas) has been lost since 1900. Broad-scale habitat mapping of the 200m wide terrestrial margin with particular emphasis on the extent of natural vegetated terrestrial margin.

Table A1.   Background information to determine susceptibility of estuaries to catchment inputs of fine sediment
Table A1. Background information to determine susceptibility of estuaries to catchment inputs of fine sediment

Estuary Characteristics 127

Estuary Characteristics & Vulnerabilities 128

Beach, Dune and Rocky Shore: Characteristics and Vulnerabilities 161

Broad Scale Habitat Classifications 166

Habitat maps 167

Figure

Table 1.  Coastal Monitoring Tools (Wriggle Coastal Management).
Figure 1  Tasman coastal sections and estuaries assessed in this report
Table 3.  Steps in Filling out The Vulnerability Matrix
Figure 2   Schematic diagram of coastal circulation patterns in the Tasman region (adapted from  Tuckey et al  2006)
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References

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