River and stream water quality and ecology - Greater Wellington ...
River and stream water quality and ecology - Greater Wellington ...
River and stream water quality and ecology - Greater Wellington ...
You also want an ePaper? Increase the reach of your titles
YUMPU automatically turns print PDFs into web optimized ePapers that Google loves.
<strong>River</strong> <strong>and</strong> <strong>stream</strong> <strong>water</strong> <strong>quality</strong> <strong>and</strong> <strong>ecology</strong> in the <strong>Wellington</strong> region: State <strong>and</strong> trends<br />
5. Periphyton – state <strong>and</strong> trends<br />
This section assesses state <strong>and</strong> trends in periphyton growth in river <strong>and</strong> <strong>stream</strong>s<br />
across the <strong>Wellington</strong> region, based on monitoring results from the 46 RSoE<br />
sites which have gravel/cobble substrates suitable for periphyton growth.<br />
Assessment of the current state of periphyton growth is presented first, using<br />
cover <strong>and</strong> biomass measurements collected over the period July 2008 to June<br />
2011. Brief comment is also provided on macrophyte cover present at the nine<br />
RSoE sites with beds dominated by soft sediment. Temporal trends in<br />
periphyton cover <strong>and</strong> biomass are then examined for the period September 2003<br />
to June 2011.<br />
5.1 State<br />
5.1.1 Approach to analysis<br />
The current state of periphyton growth was assessed at the 46 hard substrate<br />
RSoE sites using two data sets: monthly observations of percent periphyton<br />
<strong>stream</strong>bed cover from July 2008 to June 2011 <strong>and</strong> periphyton biomass<br />
(represented by chlorophyll a concentration) from annual biological sampling<br />
during the 2009, 2010 <strong>and</strong> 2011 summer/autumn periods. These data sets were<br />
compared against the MfE (2000) New Zeal<strong>and</strong> periphyton guideline values.<br />
The MfE (2000) guidelines identify periphyton cover <strong>and</strong> biomass thresholds<br />
to protect a number of different in<strong>stream</strong> values (Table 5.1).<br />
Table 5.1: MfE (2000) guidelines used to assess periphyton <strong>stream</strong> bed cover <strong>and</strong><br />
biomass at 46 RSoE sites<br />
Periphyton cover (% cover)<br />
Periphyton<br />
In<strong>stream</strong> value<br />
Mat >0.3 cm thick Filamentous >2 cm long<br />
biomass<br />
(mg/m2 )<br />
Aesthetics/recreation 60% 30% –<br />
Benthic biodiversity – – 50<br />
Trout habitat <strong>and</strong> angling – 30% 120<br />
To facilitate inter-site comparisons of overall periphyton growth <strong>and</strong> to help<br />
summarise where periphyton growth may be an issue, each RSoE site was<br />
categorised into one of four classes ranging from ‘poor’ to ‘excellent’. The<br />
classes were identified by assessing the number or percentage of guideline<br />
exceedances using a combination of both monthly <strong>stream</strong>bed cover <strong>and</strong> annual<br />
biomass data (Table 5.2). Mean periphyton cover <strong>and</strong> percent compliance with<br />
guideline values were calculated based on the total number of times a site was<br />
visited rather than the number of periphyton cover assessments able to be<br />
made. This is because the majority of instances in which periphyton cover<br />
could not be assessed coincided with high river or <strong>stream</strong> flows when<br />
periphyton cover was likely to be minimal/below guidelines.<br />
Relationships between mean <strong>and</strong> maximum periphyton cover/biomass,<br />
up<strong>stream</strong> l<strong>and</strong>cover <strong>and</strong> a range of environmental variables were also assessed<br />
using Spearman Rank correlations with a significance threshold of p
Change language