Fremantle Port Inner Harbour and Channel ... - Fremantle Ports

4. Environmental Quality Indicators and Targets
4.1. Water Quality
4.1.1. Ecosystem Health (EQO1: Maintenance of Ecosystem Integrity)
Light requirements for Seagrass and Coral Health
Water quality triggers will be based on light attenuation in the water column, related to the
minimum light requirements (MLR) of seagrass and corals, as described in the DSDMP
(Fremantle Ports, 2009). Specifically, the Light Attenuation Coefficient (LAC), a measure of
the attenuation of light with depth through the water column, will be assessed against trigger
values that are specific to depth, habitat (seagrass or corals) and BPPH management zones.
The higher the LAC, the less light that can penetrate the water column to reach
photosynthesising BPP, such as seagrass and corals.
Water quality triggers for each level of management response (see Section 5.1.1 – Seagrass
and Coral Health) are based on a stepwise percentage increase above the LAC that was used
to determine the inner boundary of the BPPH management zone being monitored. The
predicted Zone of Loss (ZoL) is not included in management response, since any BPPH within
the ZoL is assumed to be lost through physical disturbance (within the dredging and disposal
footprints) or high turbidity and sedimentation immediately adjacent to Project activities.
Table 4.1 presents the triggers developed during the environmental impact assessment
(Fremantle Ports, 2009) for each management response level (Levels 1-4) with example LAC
trigger levels for a hypothetical monitoring site within a seagrass community at 10 m depth.
Actual trigger values to be applied at monitoring sites within the ZoI or ZoE have been
calculated for one metre depth intervals for:
1. Seagrass sites: based on a 10% MLR of the most sensitive species (Posidonia
sinuosa) (Table 4.2); and
2. Coral sites: based on a 20% MLR - the light requirements obtained from the
literature for coral taxa present at Hall Bank (Cooper, et al., 2007) (Table 4.3).
Further rationale regarding the development and application of LAC trigger values is provided
within the DSDMP (Fremantle Ports 2009).
Table 4.1
Water Quality Triggers for each Level of Management Response within the Zone of
Influence (ZoI) and Zone of Effect (ZoE)
Management
Response
Level
Trigger
Example LAC trigger levels
(for a seagrass site at 10m depth)
ZoI ZoE ZoI ZoE
No Exceedance LAC0.100
Level 2
Level 3
Level 4
LAC>trigger
for >21 days
LAC>trigger
for >4 wks
LAC>trigger
for >6 wks
LAC 30% higher
than trigger
LAC 40% higher
than trigger
LAC 50% higher
than trigger
LAC>0.100
for >21 days
LAC>0.100
for >4 wks
LAC>0.100
for >6 wks
LAC>0.130
LAC>0.140
LAC>0.150
10 Oceanica: Fremantle Ports: Inner Harbour and Channel Deepening - Water Quality Monitoring Program