What NEAP Does

NEAP User Outputs

For a given waterbody (impoundment, lake or lacustrine wetland), NEAP can provide the NEAP-user with one or more of the following eutrophication-related outputs, viz:

1. Determination of the total phosphorus loading to the waterbody ‘back-calculated’ from a known in-lake condition (=EXTERNAL LOADING BACK-CALCULATION MODULE);
2. For known phosphorus load(s), prediction of the in-lake ambient phosphorus, supporting comparison of predicted vs observed conditions (=PHOSPHORUS LOADING MODULE);
3. Prediction of the mean annual in-lake P concentration, based on the output from the Phosphorus Loading Module (=IN-LAKE CONDITION MODULE);
4. Prediction of the concentration of chlorophyll-a likely to be associated with the mean annual and total P concentrations predicted by the Phosphorus Loading Module (=CHLOROPHYLL PREDICTION MODULE);
5. Characterization of the trophic condition of the waterbody, using two approaches, viz. Trophic State Index and/or Fixed Boundary conditions (=TROPHIC STATE PREDICTION MODULE);
6. Determination of the change in in-lake condition following a reduction in loading (=LOAD REDUCTION MODULE);
7. Prediction of the eutrophication risk associated with a particular waterbody (=RISK ASSESSMENT MODULE). Activation of this module will follow testing of the NEAP beta-version (i.e. it is not made available in NEAP V1.0).

Examples (see also the Worked Example included the DOWNLOADS section):

EXTERNAL LOADING BACK-CALCULATION MODULE: If the NEAP-user is reasonably confident of the mean annual in-lake concentration of phosphorus, as total phosphorus, then this module will generate the total load of phosphorus that would be expected to produce the observed conditions. If the user also has the area of catchment for the waterbody under consideration, this module will also generate a P-export coefficient for the entire catchment, as a mass per m2. Obviously this level of resolution cannot disaggregate between different types of landuse within the greater catchment area.

PHOSPHORUS LOADING MODULE: This module allows the NEAP-user to input all known phosphorus loads, either known or estimated from the product of landuse (by area) and an export coefficient. It also allows the user to input the volume component of point source loadings such as those from wastewater treatment works. The module outputs the predicted in-lake condition, as a mean annual total phosphorus concentration, which may then be compared with the observed value, and/or used for predictions of additional loadings or load reductions.

If the NEAP-user wishes to determine the impact of additional loads to an existing lake, and does not have the current total loading, this can first be determined using the External Loading Back-Calculation Module – the output from which is used as akin to a point-source input in the Phosphorus Loading Module. Additional modules predict the concentration of chlorophyll that is associated with the predicted phosphorus concentration, and the Trophic State, as an index or boundary-limited value.

IN-LAKE CONDITION MODULE: This module processes the output from the Phosphorus Loading Module to generate a predicted mean annual TP for the waterbody being considered. If the observed value is entered in this module an additional output, namely the difference between observed and predicted is provided as the simple difference of the two values.

CHLOROPHYLL PREDICTION MODULE: This module employs the output from the In-Lake Condition Module, together with the lake depth (entered in the hydrologic module) to predict the mean annual concentration of chlorophyll-a that can be anticipated. The module also estimates what the maximum P is likely to be at the height of the growing season.

TROPHIC STATE PREDICTION MODULE: This module provides the NEAP-user with an indication of how much the effects of eutrophication are impacting on the waterbody being considered. The module requires that one or more of three possible inputs be provided by the user, viz.

• Mean annual total P (units)
• Mean annual chlorophyll-a (units)
• Mean annual water transparency (Secchi Disk, m)*

* the transparency module is not fully supported in NEAP V1.0 and has been included for testing only using user-selected values.

Alternatively the program employs the outputs from the In-Lake Condition and Chlorophyll Prediction Modules to generate the TSI values.

Two module outputs are generated:

1. A Trophic State Index (TSI) value, a value on a scale starting at 0 and which is open-ended. On this log-based scale an increase of 10 TSI units will represent a doubling of algal biomass;
2. The trophic condition (oligo, meso, eutrophic or hypertrophic) as compared with the fixed boundary conditions of the OECD rating scheme. These outputs are further qualified by their proximity to a trophic condition boundary i.e. mesotrophic (High) would be close to the meso-eutrophic boundary condition.

Later versions of NEAP will generate these outputs graphically against a background of values for various South African waterbodies.

PHOSPHORUS LOADING REDUCTION MODULE: Use of this module assumes that the NEAP-user has created an in-lake condition using the In-Lake Condition Module. The user then enters a required load reduction (as a percentage) whereupon the module generates the required load reduction in kg, and generates a new in-lake condition relevant to the new conditions.

RISK ASSESSMENT MODULE: Not available in Beta version.

Steps for using NEAP

In order to be able to generate any or all of the NEAP outputs, the NEAP-user must first create the waterbody by entering a suite of geographic and hydro-geomorphological data (=CREATE A LAKE MODULE – see HOW TO USE NEAP). Various support and additional information queries may be accessed/answered depending on the module and the stage of development of NEAP. Each waterbody so created is allocated a unique code by NEAP, and is stored in a database for later retrieval by the NEAP-user. Thereafter use of any of the four OUTPUT modules will necessitate further data entry relevant to the desired output. These data inputs are requested by the programme as and when required.

On request NEAP generates a Data Requirements checklist that allows the NEAP-user to assemble the required inputs for subsequent entry into the programme. Subsequent versions of NEAP will generate this list as a spreadsheet file that can be imported directly back into NEAP – thereby offsetting the need to key in individual entries.

NEAP Development Outputs

NEAP provides information to both the NEAP-user and to the developer. In this regard certain data entered into NEAP will be used to determine optimal load-response relationships, as well as to refine appropriate export coefficients for catchments and landuse types. This information will be employed in future NEAP revisions.