Laugharne Estuary Comprehensive September 2026 Water Quality & Incident Report

cha3480

19 hours ago

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Monitoring during September 2026 revealed an event across the Laugharne Estuary, reversing August’s clean baseline. Initial testing on 18 September recorded a Phosphate surge (1.34 mg/L) and an acidic drop in marine pH (6.9). Targeted re-testing on 21September at 15:30 recorded an Ammonia spike of 1.64 mg/L at Frog Rock (SN 30516 10348,~40m from the STW outfall).

We have asked NRW and Dwr Cymru to investigate.

Key Findings from 21 September 2026 Follow-Up

Acute Ammonia Spike at Frog Rock (1.64 mg/L): Ammonia at Frog Rock surged from 0.45 mg/L to 1.64 mg/L (over 16x above baseline).

Downstream Nitrogen Transformation (1.29 mg/L Nitrate): Nitrate LR at Path by Steps jumped from 0.39 mg/L to 1.29 mg/L (3.3x increase).

Phosphate Flushing (1.34 mg/L → 0.11 mg/L): Phosphate at Frog Rock dropped back down near normal high-tide baseline as phosphate diluted or bound to sediment following the 18 September peak.

Recovery of Tidal pH Buffer (pH 7.8): Marine pH increased to 7.8 at both locations up from pH 6.9 observed three days prior.

Combined Key Findings & Slack-Tide Discharge Event.

Initial Phosphate Acidic Flush (18 Sept): Phosphate spiked to 1.34 mg/L at Frog Rock (requiring a 50/50 dilution) and 0.58 mg/L upstream at Path by Steps (SN 30603 11000) alongside an acidic drop to pH 6.9–7.0.

Upstream Catchment Pressure (21 Sept): Nitrate LR upstream at Path by Steps jumped to 1.29 mg/L (up from 0.39 mg/L).

2. September Incident Comparison: Initial (18/09) vs. Follow-Up (21/09)

Sampling Site	Parameter	18/09/2026	21/09/2026	Baseline Target	Incident Trend & Assessment
Path by Steps	Ammonia (mg/L)	0.60	0.42	< 0.10	📉 Easing but elevated
(SN 30603 11000 - Upstream)	Phosphate (mg/L)	0.58	0.19	< 0.10	📉 Dropping toward baseline
	pH	7.0	7.8	7.8 – 8.2	🟢 Saline buffer restored
	Nitrate LR (mg/L)	0.39	1.29	< 0.90	🚨 Upstream catchment spike
Frog Rock	Ammonia (mg/L)	0.45	1.64	< 0.10	🚨 Severe point-source spike (16x baseline)
(SN 30516 10348 - STW Outfall)	Phosphate (mg/L)	1.34*	0.11	< 0.10	📉 Flushed back to baseline
	pH	6.9	7.8	7.8 – 8.2	🟢 Saline buffer restored
	Nitrate LR (mg/L)	0.59	0.75	< 0.90	📈 Mild increase