All posts by Keith Hamill

Bay of Plenty River Water quality: State and Trends

River Lake has been working with Bay of Plenty Regional Council to complete a report on the state and trends of water quality in Bay of Plenty rivers.

Over the ten year period 2009 to 2018 the Bay of Plenty river monitoring sites have shown overall worsening trends for total phosphorus (TP), dissolved reactive phosphorus (DRP) and nitrate (NNN); but overall improving trends for absorbance (A440), total ammonia (NH4-N) and electrical conductivity.

The trend results are shown in the graphs below:

River water quality trends 2009-2018
River water quality trends 2009 – 2018
The proportion of BOP river monitoring sites with improving trends (PIT) for selected variables.

The full report can be downloaded from here:

Otamakaukau Awatapu Lagoon Restoration

Awatapu Lagoon restoration planting, October 2019.

River Lake is supporting the Otamakaukau Kaitiaki Trust to restore the mauri of Awatapu Lagoon, Whakatane . We are starting with riparian planting. So far this spring 2019, 45 community volunteers have helped plant 2500 wetland plants and install a small floating nursery.

This project is a partnership between Otamakaukau Kaitiaki Trust and Halo Whakatane. It is supported by the Bay of Plenty Regional Council Environmental Enhancement Fund.

Awatapu 2019: The first wetland plants in the ground.
Awatapu planting day, October 2019

Phosphorus loads to Lake Rotorua

 What is the phosphorus load to Lake Rotorua and how much comes from human activity?

River Lake revised estimates of P loads to Lake Rotorua to account for groundwater catchment areas, geothermal inputs and long-term average loads.

This work contributed to the Science Review required by Plan Change 10 of the Bay of Plenty Regional Water and Land Plan (RWLP).

Read the report here:

Hamill KD 2018. Anthropogenic Phosphorus Load to Rotorua Review and Revision. Prepared for Bay of Plenty Regional Council by River Lake Ltd

Kaituna River Mixing Study

River Lake studied the mixing of diagonal drain pump station with the lower Kaituna River. We used Rhotomine dye WT to understand how well the pump station discharge mixed across the Kaituna River before the intake for the new diversion to Maketū Estuary.

The work was done for Bay of Plenty Regional Council rivers and drainage team.

Rhodamine WT dye entering the Kaituna River from the Diagonal Drain pump station, 2.3 km upstream from the river mouth (9 Nov 2017). Photo by Andy Belcher.
Lower Kaituna River facing towards Maketū Estuary. The borrow pits are visible on the true right of the river. At this location discharges from Diagonal Drain had mixed across 50% to 70% of the river, depending on the tide (9 November 2017). Photo by Andy Belcher.

Setting nutrient limits

Waituna Lagoon, Southland

Setting nutrient limits for complex ecosystems is challenging. We used multiple lines of evidence to set robust nutrient limits to safeguard the macrophyte community in Waituna Lagoon.

Read more in our paper on setting nutrient limits for lakes (click the link below).

Schallenberg et al 2017 Multiple lines of evidence determine robust nutrient load limits required to safeguard a threatened lake lagoon system