See Hickson-Rowden and Perrie (2018) for the finer details on the application of the assessments outlined below
Classification of lake trophic status using the TLI Burns et al. (1999).
| Trophic status (nutrient enrichment) | TLI | Chlorophyll a (mg/m3) | Secchi depth (m) | Total phosphorus (g/m3) | Total nitrogen (g/m3) |
|---|---|---|---|---|---|
| Ultra-microtrophic (practically pure) | 0.0-1.0 | 0.13-0.33 | 33-25 | 0.00084-0.0018 | 0.016-0.034 |
| Microtrophic (very low) | 1.0-2.0 | 0.33-0.82 | 25-13 | 0.0018-0.0041 | 0.034-0.073 |
| Oligotrophic (low) | 2.0-3.0 | 0.82-2.0 | 15-7.0 | 0.0041-0.0090 | 0.073-0.157 |
| Mesotrophic (medium) | 3.0-4.0 | 2.0-5.0 | 7.0-2.8 | 0.0090-0.0200 | 0.157-0.337 |
| Eutrophic (high) | 4.0-5.0 | 5.0-12 | 2.8-1.1 | 0.0200-0.0430 | 0.337-0.725 |
| Supertrophic (very high) | 5.0-6.0 | 12-31 | 1.1-0.4 | 0.0430-0.0960 | 0.725-1.558 |
| Hypertrophic (extremely high) | >6.0 | >31 | <0.4 | >0.0960 | >1.558 |
Selected attributes and narratives from Table 3.5 of GW’s NRP. Note that monitoring data should be analysed separately for closed periods and open periods for intermittently closed and open lakes or lagoons (ICOLLs), such as Lake Ōnoke.
| Attribute | Lake type | Annual summary | Threshold |
|---|---|---|---|
| Total Nitrogen (mg/m3) | Seasonally stratified and brackish | Median | ≤350 |
| Polymictic | Median | ≤500 | |
| Total Phosphorus (mg/m3) | Median | ≤20 | |
| Phytoplankton (mg chl-a/m3) | Median | ≤5 | |
| Max | ≤25 |
Attribute states and guideline values are taken from the National Policy Statement for Freshwater Management 2020 National Objectives Framework (NOF). For Lake Ōnoke that is intermittently open to the sea, monitoring data should be analysed separately for closed periods and open periods.
| Attribute state | Annual median | Annual maximum | Description |
|---|---|---|---|
| A | ≤2 | ≤10 | Lake ecological communities are healthy and resilient, similar to natural reference conditions. |
| B | >2 and >5 | >10 and >25 | Lake ecological communities are slightly impacted by additional algal and/or plant growth arising from nutrient levels that are elevated above natural reference conditions. |
| C | >5 and >12 | >25 and >60 | Lake ecological communities are moderately impacted by additional algal and plant growth arising from nutrient levels that are elevated well above natural reference conditions. Reduced water clarity is likely to affect habitat available for native macrophytes. |
| D | >12 | >60 | National bottom line. Lake ecological communities have undergone or are at high risk of a regime shift to a persistent, degraded state (without native macrophyte/seagrass cover), due to impacts of elevated nutrients leading to excessive algal and/or plant growth, as well as from losing oxygen in bottom waters of deep lakes. |
| Attribute state | Annual median | Description |
|---|---|---|
| A | ≤10 | Lake ecological communities are healthy and resilient, similar to natural reference conditions. |
| B | >10 and >20 | Lake ecological communities are slightly impacted by additional algal and/or plant growth arising from nutrient levels that are elevated above natural reference conditions. |
| C | >20 and >50 | Lake ecological communities are moderately impacted by additional algal and plant growth arising from nutrient levels that are elevated well above natural reference conditions. |
| D | >50 | National bottom line. Lake ecological communities have undergone or are at high risk of a regime shift to a persistent, degraded state (without native macrophyte/seagrass cover), due to impacts of elevated nutrients leading to excessive algal and/or plant growth, as well as from losing oxygen in bottom waters of deep lakes. |
Attribute states are calculated differently for polymictic lakes (polymictic) and seasonally stratified & brackish lakes (brackish). See this Land Air Water Aotearoa (LAWA) factsheet for more information.
| Attribute state | Annual median (polymictic) | Annual median (brackish) | Description |
|---|---|---|---|
| A | ≤300 | ≤160 | Lake ecological communities are healthy and resilient, similar to natural reference conditions. |
| B | >300 and >500 | >160 and >350 | Lake ecological communities are slightly impacted by additional algal and/or plant growth arising from nutrient levels that are elevated above natural reference conditions. |
| C | >500 and >800 | >350 and >750 | Lake ecological communities are moderately impacted by additional algal and plant growth arising from nutrient levels that are elevated well above natural reference conditions. |
| D | >800 | >750 | National bottom line. Lake ecological communities have undergone or are at high risk of a regime shift to a persistent, degraded state (without native macrophyte/seagrass cover), due to impacts of elevated nutrients leading to excessive algal and/or plant growth, as well as from losing oxygen in bottom waters of deep lakes. |
Numeric attribute state is based on pH 8 and temperature of 20°C.
| Attribute state | Annual median | Annual 95th percentile | Description |
|---|---|---|---|
| A | ≤0.03 | ≤0.05 | 99% species protection level: No observed effect on any species tested. |
| B | >0.03 and >0.24 | >0.05 and >0.4 | 95% species protection level: Starts impacting occasionally on the 5% most sensitive species. |
| C | >0.24 and >1.3 | >0.4 and >2.2 | National bottom line. 80% species protection level: Starts impacting regularly on the 20% most sensitive species (reduced survival of most sensitive species). |
| D | >1.3 | >2.2 | Starts approaching acute impact level (that is, risk of death) for sensitive species. |
Trends assessments are estimated at each site using monthly data over periods of 5-, 10-, and 15- years, where sufficient data is available. These results are then categorised into differing levels of trend direction likelihood. Series with too many censored values (refer to the lab detection limits table) can still have a trend direction estimated but are unable to have a reliable trend rate estimated and this is shown as ‘N/A’ in the map hover labels and tables. Site-periods with too few data for reliable estimates of both direction and rate are shown as “not assessed”.
The trend methodology follows the approach as described in this LAWA trends factsheet with exceptions