This study employed in situ, self-developed two-dimensional miniaturized diffusive gradients in thin films (2D-MDGT) and planar optode (PO) techniques to simultaneously measure labile phosphorus (Labile P), soluble reactive phosphorus (SRP), ammonium (NH4+-N), nitrite (NO2--N), and nitrate (NO3--N) in sediments of Lake Ulansuhai, along with microenvironmental parameters (pH and dissolved oxygen) across the sediment-water interface (SWI) during both freezing and unfreezing periods. The results revealed significant spatiotemporal heterogeneity in the concentrations of these solutes. During the freezing period, mean concentrations were (0.006 ± 0.005) mg/L for Labile P, (0.096 ± 0.070) mg/L for SRP, (2.70 ± 0.50) mg/L for NH4+-N, (0.150 ± 0.061) mg/L for NO2--N, and (0.48 ± 0.48) mg/L for NO3--N, all significantly lower than those during the unfreezing period ((0.060 ± 0.036）mg/L, (0.15 ± 0.16) mg/L, (24.0 ± 1.7) mg/L, (0.36 ± 0.042) mg/L, and (1.4 ± 1.1) mg/L, respectively). Vertically, Labile P, SRP, and NH4+-N concentrations increased with sediment depth, while NO3--N decreased; NO2--N showed no consistent vertical trend. Horizontally, higher nitrogen and phosphorus concentrations were observed in the northern region, due to greater sediment accumulation and intensified reductive conditions. The in situ exchange fluxes across the SWI ranged from -0.32 to 26 μg/(m2·d) for Labile P, -3.9 to 36 μg/(m2·d) for SRP, -18 to 6.9 mg/(m2·d) for NH4+-N, -1.5 to 8.0 mg/(m2·d) for NO2--N, and -0.22 to 0.16 mg/(m2·d) for NO3--N. Notably, the unfreezing period exhibited significantly higher release fluxes of nitrogen and phosphorus, substantially increasing the risk of internal nutrient loading and eutrophication in Lake Ulansuhai.